Use llvm-ar when building with Clang.

build/config/compiler/BUILD.gn

Index: build/config/compiler/BUILD.gn
diff --git a/build/config/compiler/BUILD.gn b/build/config/compiler/BUILD.gn
index 0419926d127955f5dd7b7b0ff245b8d90e46effc..939c8e29703ef87a7bc463910219b90acb83f584 100644
--- a/build/config/compiler/BUILD.gn
+++ b/build/config/compiler/BUILD.gn
@@ -166,11 +166,6 @@ config("compiler") {
     configs += [ "//build/config/mac:compiler" ]
   }
 
-  # Applies to all Posix systems.
-  if (is_posix) {
-    configs += [ "//build/config/posix:compiler" ]
-  }
-
   # See the definitions below.
   configs += [
     ":compiler_cpu_abi",
@@ -303,17 +298,11 @@ config("compiler") {
   # ---------------------------------
   if (is_linux || is_android) {
     if (use_pic) {
-      cflags += [
-        "-fPIC",
-      ]
-      ldflags += [
-        "-fPIC",
-      ]
+      cflags += [ "-fPIC" ]
+      ldflags += [ "-fPIC" ]
     }
 
-    cflags += [
-      "-pipe",  # Use pipes for communicating between sub-processes. Faster.
-    ]
+    cflags += [ "-pipe" ]  # Use pipes for communicating between sub-processes. Faster.

[Nico, 2017/03/27 17:10:39]

Nit: put comment above += line (yes, not your code)

[krasin1, 2017/03/27 17:51:23]

Done.

 
     ldflags += [
       "-Wl,-z,noexecstack",