Build 64bit browser for Android with clang for ARMv8

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 76a42eb399d573f7fce1ad3c5897554af7ce640b..c3ab9994a5b4f31743f0afc23efac06dc7dfcc5b 100644
--- a/build/config/compiler/BUILD.gn
+++ b/build/config/compiler/BUILD.gn
@@ -8,7 +8,7 @@ import("//build/config/compiler/compiler.gni")
 import("//build/config/nacl/config.gni")
 import("//build/toolchain/cc_wrapper.gni")
 
-if (current_cpu == "arm") {
+if (current_cpu == "arm" || current_cpu == "arm64") {
   import("//build/config/arm.gni")
 }
 if (current_cpu == "mipsel" || current_cpu == "mips64el") {
@@ -633,6 +633,9 @@ config("compiler_arm_fpu") {
   if (current_cpu == "arm" && !is_ios && !is_nacl) {
     cflags = [ "-mfpu=$arm_fpu" ]
     asmflags = cflags
+  } else if (current_cpu == "arm64" && !is_ios && !is_nacl) {
+    cflags = [ "-mcpu=$arm_fpu" ]

[Nico, 2016/04/14 15:43:55]

the 32-bit arm branch sets -mfpu, this sets -mcpu. is that intentional?

[khasim.mohammed, 2016/04/14 16:38:46]

-mpu is a 32bit only option, for 64bit mpu is not the correct option, we should
use -mcpu. 

+    asmflags = cflags
   }
 }
 
@@ -884,6 +887,7 @@ config("default_warnings") {
 
       # TODO(hans): Get this cleaned up, http://crbug.com/428099
       "-Wno-inconsistent-missing-override",
+      "-Wno-error=unused-command-line-argument",

[Nico, 2016/04/14 15:43:55]

why is this needed?

we want a warning-free build, we don't accept -Wno-error flags. what complains
without this? can we not pass these flags instead?

[khasim.mohammed, 2016/04/14 16:38:46]

I will remove this. It is not needed.

     ]
 
     # NaCl's Clang compiler and Chrome's hermetic Clang compiler will almost
@@ -915,6 +919,7 @@ config("chromium_code") {
     if (is_clang) {
       # Enable -Wextra for chromium_code when we control the compiler.
       cflags += [ "-Wextra" ]
+      cflags += [ "-Wno-error=implicit-exception-spec-mismatch" ]
     }
 
     # In Chromium code, we define __STDC_foo_MACROS in order to get the
@@ -975,6 +980,7 @@ config("no_chromium_code") {
       # Lots of third-party libraries have unused variables. Instead of
       # suppressing them individually, we just blanket suppress them here.
       "-Wno-unused-variable",
+      "-Wno-asm-operand-widths",
     ]
   }