[sysroot] Switch to the new sysroot location

Linux sysroot is now located in build rather than buildtools.

TC-312

Change-Id: I9daa600d981b4e54b9b291a2157564ae7c83c1f8
diff --git a/config/BUILDCONFIG.gn b/config/BUILDCONFIG.gn
index a620f0b..b837b29 100644
--- a/config/BUILDCONFIG.gn
+++ b/config/BUILDCONFIG.gn
@@ -17,12 +17,15 @@
 if (target_cpu == "") {
   target_cpu = host_cpu
 }
+target_platform = "${target_os}-${target_cpu}"
 if (current_cpu == "") {
   current_cpu = target_cpu
 }
 if (current_os == "") {
   current_os = target_os
 }
+current_platform = "${current_os}-${current_cpu}"
+
 host_platform = "${host_os}-${host_cpu}"
 
 if (target_os == "fuchsia") {
diff --git a/config/sysroot.gni b/config/sysroot.gni
index 5ecde0a..1595e84 100644
--- a/config/sysroot.gni
+++ b/config/sysroot.gni
@@ -15,7 +15,7 @@
                      "target_out_dir")
   sysroot = rebase_path("$_out_dir/sysroot")
 } else if (is_linux) {
-  sysroot = rebase_path("//buildtools/${host_platform}/sysroot")
+  sysroot = rebase_path("//build/third_party/sysroot/${current_platform}")
 } else if (is_mac) {
   import("//build/config/mac/config.gni")
   sysroot = mac_sdk_path