Make goma work for the GN build on linux.

build/toolchain/linux/BUILD.gn

Index: build/toolchain/linux/BUILD.gn
diff --git a/build/toolchain/linux/BUILD.gn b/build/toolchain/linux/BUILD.gn
index 9789454e30823bf7054ffd9fb823d987d4c87b03..a98ea53c95cecd5613c24ea476ce5089f35a7702 100644
--- a/build/toolchain/linux/BUILD.gn
+++ b/build/toolchain/linux/BUILD.gn
@@ -7,9 +7,16 @@ import("//build/toolchain/clang.gni")
 import("//build/toolchain/gcc_toolchain.gni")
 import("//build/toolchain/goma.gni")
 
+if (use_goma) {
+  goma_prefix = "$goma_dir/gomacc "
+} else {
+  goma_prefix = ""
+}
+
 gcc_toolchain("arm") {
-  cc = "arm-linux-gnueabi-gcc"
-  cxx = "arm-linux-gnueabi-g++"
+  cc = "${goma_prefix}arm-linux-gnueabi-gcc"
+  cxx = "${goma_prefix}arm-linux-gnueabi-g++"

[Dirk Pranke, 2014/07/17 01:18:27]

this seemed like the safest and clearest approach to me, but perhaps you might
have other ideas. 

+
   ar = "arm-linux-gnueabi-ar"
   ld = cxx
 
@@ -26,8 +33,8 @@ gcc_toolchain("clang_x86") {
     prefix = rebase_path("//third_party/llvm-build/Release+Asserts/bin",
                          root_build_dir)
   }
-  cc = "$prefix/clang"
-  cxx = "$prefix/clang++"
+  cc = "${goma_prefix}$prefix/clang"
+  cxx = "${goma_prefix}$prefix/clang++"
 
   ar = "ar"
   ld = cxx
@@ -38,8 +45,8 @@ gcc_toolchain("clang_x86") {
 }
 
 gcc_toolchain("x86") {
-  cc = "gcc"
-  cxx = "g++"
+  cc = "${goma_prefix}gcc"
+  cxx = "$goma_prefix}g++"
 
   ar = "ar"
   ld = cxx
@@ -57,8 +64,8 @@ gcc_toolchain("clang_x64") {
     prefix = rebase_path("//third_party/llvm-build/Release+Asserts/bin",
                          root_build_dir)
   }
-  cc = "$prefix/clang"
-  cxx = "$prefix/clang++"
+  cc = "${goma_prefix}$prefix/clang"
+  cxx = "${goma_prefix}$prefix/clang++"
 
   ar = "ar"
   ld = cxx
@@ -69,8 +76,8 @@ gcc_toolchain("clang_x64") {
 }
 
 gcc_toolchain("x64") {
-  cc = "gcc"
-  cxx = "g++"
+  cc = "${goma_prefix}gcc"
+  cxx = "${goma_prefix}g++"
 
   ar = "ar"
   ld = cxx