GN: avoid going through compiler wrapper for "link" tool for macOS/iOS.

build/toolchain/mac/BUILD.gn

 # Copyright (c) 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # TODO(brettw) Use "gcc_toolchain.gni" like the Linux toolchains. This requires
 # some enhancements since the commands on Mac are slightly different than on
 # Linux.
 
 import("../goma.gni")
 import("//build/config/clang/clang.gni")
@@ skipping 65 matching lines @@
       # Populate toolchain args from the invoker.
       forward_variables_from(invoker.toolchain_args, "*")
 
       # The host toolchain value computed by the default toolchain's setup
       # needs to be passed through unchanged to all secondary toolchains to
       # ensure that it's always the same, regardless of the values that may be
       # set on those toolchains.
       host_toolchain = host_toolchain
     }
 
+    # Supports building with the version of clang shipped with Xcode when
+    # targetting iOS by not respecting clang_base_path.
+    if (toolchain_args.current_os == "ios" && use_xcode_clang) {
+      prefix = ""
+    } else {
+      prefix = rebase_path("$clang_base_path/bin/", root_build_dir)
+    }
+
+    _cc = "${prefix}clang"
+    _cxx = "${prefix}clang++"
+
     # When the invoker has explicitly overridden use_goma or cc_wrapper in the
     # toolchain args, use those values, otherwise default to the global one.
     # This works because the only reasonable override that toolchains might
     # supply for these values are to force-disable them.
     if (defined(toolchain_args.use_goma)) {
       toolchain_uses_goma = toolchain_args.use_goma
     } else {
       toolchain_uses_goma = use_goma
     }
     if (defined(toolchain_args.cc_wrapper)) {
       toolchain_cc_wrapper = toolchain_args.cc_wrapper
     } else {
       toolchain_cc_wrapper = cc_wrapper
     }
 
     # Compute the compiler prefix.
     if (toolchain_uses_goma) {
       assert(toolchain_cc_wrapper == "",
              "Goma and cc_wrapper can't be used together.")
       compiler_prefix = "$goma_dir/gomacc "
     } else if (toolchain_cc_wrapper != "") {
       compiler_prefix = toolchain_cc_wrapper + " "
     } else {
       compiler_prefix = ""
     }
 
-    if (toolchain_args.current_os != "ios" || !use_xcode_clang) {
-      compiler_prefix += rebase_path("$clang_base_path/bin/", root_build_dir)
-    }
-
-    cc = "${compiler_prefix}clang"
-    cxx = "${compiler_prefix}clang++"
-    ld = cxx
+    cc = compiler_prefix + _cc
+    cxx = compiler_prefix + _cxx
+    ld = _cxx
 
     linker_driver =
         "TOOL_VERSION=${tool_versions.linker_driver} " +
         rebase_path("//build/toolchain/mac/linker_driver.py", root_build_dir)
 
     # On iOS, the final applications are assembled using lipo (to support fat
     # builds). The correct flags are passed to the linker_driver.py script
     # directly during the lipo call.
     if (toolchain_args.current_os != "ios") {
       _enable_dsyms = enable_dsyms
@@ skipping 324 matching lines @@
     }
   }
 
   mac_toolchain("ios_clang_x64") {
     toolchain_args = {
       current_cpu = "x64"
       current_os = "ios"
     }
   }
 }