Correct libc path for cross-compiled pm_build

The "pm_build" step was not using the proper libc location when cross
compiling. The libc location was previously hardcoded with "x64" in it.
Here is an example output of an error observed:

Change-Id: Ibe78e25da26d5bfb7cfc91447f262c90c35bba1e
Reviewed-by: Rob Tsuk <>
diff --git a/src/ b/src/
index f3d4f62..51707c5 100644
--- a/src/
+++ b/src/
@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 use crate::{
+    get_user_libc_path,
         amber_path, cmc_path, fuchsia_dir, package_manager_path, shared_libraries_path,
         FuchsiaConfig, TargetOptions,
@@ -176,7 +177,7 @@
     let target_out_path_str = target_out_path.to_string_lossy();
     let shared_lib_path = shared_libraries_path(target_options)?;
     let shared_lib_str = shared_lib_path.to_string_lossy();
-    let libc_path = format!("{}/user.libc_x64/", target_out_path_str);
+    let libc_path = format!("{}/", get_user_libc_path(target_options)?.to_string_lossy());
     let fdio_path = format!("{}/", shared_lib_str);
     let libsyslog_path = format!("{}/", shared_lib_str);
     let libtraceengine_path = format!("{}/", shared_lib_str);