[iOS/GN] Allow compilation with system clang.

build/toolchain/toolchain.gni

Index: build/toolchain/toolchain.gni
diff --git a/build/toolchain/toolchain.gni b/build/toolchain/toolchain.gni
index 9f564794816655edd06d110aeb2ce14390f037bb..63656cf642358d5407cddbac3674ae8e60889484 100644
--- a/build/toolchain/toolchain.gni
+++ b/build/toolchain/toolchain.gni
@@ -26,6 +26,11 @@ declare_args() {
     # Clang compiler version. Clang files are placed at version-dependent paths.
     clang_version = "3.9.0"
   }
+
+  # Compile with system version of clang instead of hermetic version shipped
+  # with the build. Used on iOS to ship official builds (as they are built
+  # with the version of clang shipped with Xcode).
+  use_system_clang = is_ios && is_official_build

[Nico, 2016/06/21 13:25:44]

xcode, not system

[sdefresne, 2016/06/21 13:44:22]

Done, and made the variable conditional on host_os == "mac".

 }
 
 # Subdirectory within root_out_dir for shared library files.