Apply -fno-tree-sra and -fno-caller-saves only to Android

I don't know why http://crrev.com/293913 has moved these flags outside
if(is_android),
but the corresponding GYP code (build/config.gypi) is still applying
these flags only to Android.

BUG=433082

Review URL: https://codereview.chromium.org/1807163002

Cr-Commit-Position: refs/heads/master@{#381890}

build/config/compiler/BUILD.gn

@@ -594,7 +594,7 @@ config("compiler_codegen") {
         ]
       }
     } else if (current_cpu == "arm") {
-      if (!is_clang) {
+      if (is_android && !is_clang) {
         # Clang doesn't support these flags.
         cflags += [
           # The tree-sra optimization (scalar replacement for