diff --git a/src/librustc_codegen_ssa/back/command.rs b/src/librustc_codegen_ssa/back/command.rs
index 2c2ede5..2d84d67 100644
--- a/src/librustc_codegen_ssa/back/command.rs
+++ b/src/librustc_codegen_ssa/back/command.rs
@@ -15,6 +15,7 @@
     program: Program,
     args: Vec<OsString>,
     env: Vec<(OsString, OsString)>,
+    env_remove: Vec<OsString>,
 }
 
 #[derive(Clone)]
@@ -42,6 +43,7 @@
             program,
             args: Vec::new(),
             env: Vec::new(),
+            env_remove: Vec::new(),
         }
     }
 
@@ -81,6 +83,17 @@
         self.env.push((key.to_owned(), value.to_owned()));
     }
 
+    pub fn env_remove<K>(&mut self, key: K) -> &mut Command
+        where K: AsRef<OsStr>,
+    {
+        self._env_remove(key.as_ref());
+        self
+    }
+
+    fn _env_remove(&mut self, key: &OsStr) {
+        self.env_remove.push(key.to_owned());
+    }
+
     pub fn output(&mut self) -> io::Result<Output> {
         self.command().output()
     }
@@ -106,6 +119,9 @@
         };
         ret.args(&self.args);
         ret.envs(self.env.clone());
+        for k in &self.env_remove {
+            ret.env_remove(k);
+        }
         return ret
     }
 
diff --git a/src/librustc_codegen_ssa/back/link.rs b/src/librustc_codegen_ssa/back/link.rs
index c6e0e6a..9b044d9 100644
--- a/src/librustc_codegen_ssa/back/link.rs
+++ b/src/librustc_codegen_ssa/back/link.rs
@@ -533,6 +533,9 @@
     for &(ref k, ref v) in &sess.target.target.options.link_env {
         cmd.env(k, v);
     }
+    for k in &sess.target.target.options.link_env_remove {
+        cmd.env_remove(k);
+    }
 
     if sess.opts.debugging_opts.print_link_args {
         println!("{:?}", &cmd);
diff --git a/src/librustc_target/spec/apple_base.rs b/src/librustc_target/spec/apple_base.rs
index 53364e7..f7551aa 100644
--- a/src/librustc_target/spec/apple_base.rs
+++ b/src/librustc_target/spec/apple_base.rs
@@ -51,3 +51,19 @@
     let (major, minor) = macos_deployment_target();
     format!("{}-apple-macosx{}.{}.0", arch, major, minor)
 }
+
+pub fn macos_link_env_remove() -> Vec<String> {
+    let mut env_remove = Vec::with_capacity(2);
+    // Remove the `SDKROOT` environment variable if it's clearly set for the wrong platform, which
+    // may occur when we're linking a custom build script while targeting iOS for example.
+    if let Some(sdkroot) = env::var("SDKROOT").ok() {
+        if sdkroot.contains("iPhoneOS.platform") || sdkroot.contains("iPhoneSimulator.platform") {
+            env_remove.push("SDKROOT".to_string())
+        }
+    }
+    // Additionally, `IPHONEOS_DEPLOYMENT_TARGET` must not be set when using the Xcode linker at
+    // "/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ld",
+    // although this is apparently ignored when using the linker at "/usr/bin/ld".
+    env_remove.push("IPHONEOS_DEPLOYMENT_TARGET".to_string());
+    env_remove
+}
diff --git a/src/librustc_target/spec/apple_ios_base.rs b/src/librustc_target/spec/apple_ios_base.rs
index 6d3900c..fdbb1bd 100644
--- a/src/librustc_target/spec/apple_ios_base.rs
+++ b/src/librustc_target/spec/apple_ios_base.rs
@@ -38,9 +38,18 @@
     // SDKROOT; for rustc, the user or build system can set it, or we
     // can fall back to checking for xcrun on PATH.)
     if let Some(sdkroot) = env::var("SDKROOT").ok() {
-        let sdkroot_path = Path::new(&sdkroot);
-        if sdkroot_path.is_absolute() && sdkroot_path != Path::new("/") && sdkroot_path.exists() {
-            return Ok(sdkroot);
+        let p = Path::new(&sdkroot);
+        match sdk_name {
+            // Ignore `SDKROOT` if it's clearly set for the wrong platform.
+            "iphoneos" if sdkroot.contains("iPhoneSimulator.platform")
+                       || sdkroot.contains("MacOSX.platform") => (),
+            "iphonesimulator" if sdkroot.contains("iPhoneOS.platform")
+                              || sdkroot.contains("MacOSX.platform") => (),
+            "macosx10.15" if sdkroot.contains("iPhoneOS.platform")
+                          || sdkroot.contains("iPhoneSimulator.platform") => (),
+            // Ignore `SDKROOT` if it's not a valid path.
+            _ if !p.is_absolute() || p == Path::new("/") || !p.exists() => (),
+            _ => return Ok(sdkroot),
         }
     }
     let res = Command::new("xcrun")
@@ -100,6 +109,13 @@
     }.to_string()
 }
 
+fn link_env_remove(arch: Arch) -> Vec<String> {
+    match arch {
+        Armv7 | Armv7s | Arm64 | I386 | X86_64 => vec!["MACOSX_DEPLOYMENT_TARGET".to_string()],
+        X86_64_macabi => vec!["IPHONEOS_DEPLOYMENT_TARGET".to_string()],
+    }
+}
+
 pub fn opts(arch: Arch) -> Result<TargetOptions, String> {
     let pre_link_args = build_pre_link_args(arch)?;
     Ok(TargetOptions {
@@ -107,6 +123,7 @@
         dynamic_linking: false,
         executables: true,
         pre_link_args,
+        link_env_remove: link_env_remove(arch),
         has_elf_tls: false,
         eliminate_frame_pointer: false,
         .. super::apple_base::opts()
diff --git a/src/librustc_target/spec/i686_apple_darwin.rs b/src/librustc_target/spec/i686_apple_darwin.rs
index 7d804ea..27d0582 100644
--- a/src/librustc_target/spec/i686_apple_darwin.rs
+++ b/src/librustc_target/spec/i686_apple_darwin.rs
@@ -5,6 +5,7 @@
     base.cpu = "yonah".to_string();
     base.max_atomic_width = Some(64);
     base.pre_link_args.insert(LinkerFlavor::Gcc, vec!["-m32".to_string()]);
+    base.link_env_remove.extend(super::apple_base::macos_link_env_remove());
     base.stack_probes = true;
     base.eliminate_frame_pointer = false;
 
diff --git a/src/librustc_target/spec/mod.rs b/src/librustc_target/spec/mod.rs
index 2d8ae02..626fa37 100644
--- a/src/librustc_target/spec/mod.rs
+++ b/src/librustc_target/spec/mod.rs
@@ -581,8 +581,10 @@
     /// user-defined libraries.
     pub post_link_args: LinkArgs,
 
-    /// Environment variables to be set before invoking the linker.
+    /// Environment variables to be set for the linker invocation.
     pub link_env: Vec<(String, String)>,
+    /// Environment variables to be removed for the linker invocation.
+    pub link_env_remove: Vec<String>,
 
     /// Extra arguments to pass to the external assembler (when used)
     pub asm_args: Vec<String>,
@@ -844,6 +846,7 @@
             post_link_objects_crt: Vec::new(),
             late_link_args: LinkArgs::new(),
             link_env: Vec::new(),
+            link_env_remove: Vec::new(),
             archive_format: "gnu".to_string(),
             custom_unwind_resume: false,
             allow_asm: true,
@@ -1119,6 +1122,7 @@
         key!(post_link_objects_crt, list);
         key!(post_link_args, link_args);
         key!(link_env, env);
+        key!(link_env_remove, list);
         key!(asm_args, list);
         key!(cpu);
         key!(features);
@@ -1335,6 +1339,7 @@
         target_option_val!(post_link_objects_crt);
         target_option_val!(link_args - post_link_args);
         target_option_val!(env - link_env);
+        target_option_val!(link_env_remove);
         target_option_val!(asm_args);
         target_option_val!(cpu);
         target_option_val!(features);
diff --git a/src/librustc_target/spec/x86_64_apple_darwin.rs b/src/librustc_target/spec/x86_64_apple_darwin.rs
index 1821034..d059e44 100644
--- a/src/librustc_target/spec/x86_64_apple_darwin.rs
+++ b/src/librustc_target/spec/x86_64_apple_darwin.rs
@@ -6,6 +6,7 @@
     base.max_atomic_width = Some(128); // core2 support cmpxchg16b
     base.eliminate_frame_pointer = false;
     base.pre_link_args.insert(LinkerFlavor::Gcc, vec!["-m64".to_string()]);
+    base.link_env_remove.extend(super::apple_base::macos_link_env_remove());
     base.stack_probes = true;
 
     // Clang automatically chooses a more specific target based on