Enable ARM/linux cross compile to use clang.

build/common.gypi

Index: build/common.gypi
diff --git a/build/common.gypi b/build/common.gypi
index 58a1bf24cf67d6a7586e70039e11371f94576819..fd7b48ac3d80ed52763715b67aa480e800051b41 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -3665,26 +3665,41 @@
           ['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)',
                     ],
                   }],