Enable ARM/linux cross compile to use clang.

build/common.gypi

 # Copyright (c) 2012 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.
 
 # IMPORTANT:
 # Please don't directly include this file if you are building via gyp_chromium,
 # since gyp_chromium is automatically forcing its inclusion.
 {
   # Variables expected to be overriden on the GYP command line (-D) or by
   # ~/.gyp/include.gypi.
@@ skipping 3647 matching lines @@
                 ],
                 'ldflags': [
                   '-m64',
                 ],
               }],
             ],
           }],
           ['target_arch=="arm"', {
             'target_conditions': [
               ['_toolset=="target"', {
-                'cflags_cc': [
-                  # The codesourcery arm-2009q3 toolchain warns at that the ABI
-                  # has changed whenever it encounters a varargs function. This
-                  # silences those warnings, as they are not helpful and
-                  # clutter legitimate warnings.
-                  '-Wno-abi',
-                ],
                 'conditions': [
-                  ['arm_arch!=""', {
+                  ['clang==0', {
+                    'cflags_cc': [
+                      # The codesourcery arm-2009q3 toolchain warns at that the ABI
+                      # has changed whenever it encounters a varargs function. This
+                      # silences those warnings, as they are not helpful and
+                      # clutter legitimate warnings.
+                      '-Wno-abi',
+                    ],
+                  }],
+                  ['clang==1 and arm_arch!=""', {
+                    'cflags': [
+                      '-target <(arm_arch)-linux-gnueabihf',
+                    ],
+                  }],
+                  ['clang==1 and arm_arch!=""', {
                     'cflags': [
                       '-march=<(arm_arch)',
                     ],
                   }],
+                  ['clang==1', {
+                    'cflags': [
+                      # We need to disable clang's builtin assember and have
+                      # it use arm-linux-gnueabihf-as instead, but if I enable
+                      # this flag it currently picks /usr/bin/as :(
+                      # '-no-integrated-as',

[Nico, 2014/07/22 22:27:44]

Look at what the android build does. I think it uses -fno-integrated-as and adds
a -B flag to point at the right as (?)

[Sam Clegg, 2014/07/22 22:31:27]

Yes, but I think android cross compiler is called 'as' where as we want to use
'/usr/bin/arm-linux-gnueabihf-as'.  The sysroot we are using is a native target
sysroot that doesn't have any host tools in it so I don't think we want to point
-B at that.

I have a look at the clang sources and see if we can overide the name of that
'as' that it uses.

+                    ],
+                  }],
                   ['arm_tune!=""', {
                     'cflags': [
                       '-mtune=<(arm_tune)',
                     ],
                   }],
                   ['arm_fpu!=""', {
-                    'cflags': [
+                    'cflags_cc': [
                       '-mfpu=<(arm_fpu)',
                     ],
                   }],
                   ['arm_float_abi!=""', {
                     'cflags': [
                       '-mfloat-abi=<(arm_float_abi)',
                     ],
                   }],
                   ['arm_thumb==1', {
                     'cflags': [
@@ skipping 1957 matching lines @@
     # settings in target dicts.  SYMROOT is a special case, because many other
     # Xcode variables depend on it, including variables such as
     # PROJECT_DERIVED_FILE_DIR.  When a source group corresponding to something
     # like PROJECT_DERIVED_FILE_DIR is added to a project, in order for the
     # files to appear (when present) in the UI as actual files and not red
     # red "missing file" proxies, the correct path to PROJECT_DERIVED_FILE_DIR,
     # and therefore SYMROOT, needs to be set at the project level.
     'SYMROOT': '<(DEPTH)/xcodebuild',
   },
 }