Set default cross compiler for ARM/linux builds.

build/common.gypi

Index: build/common.gypi
diff --git a/build/common.gypi b/build/common.gypi
index ef1ce1539735ae4c30880c0bc390bc5f4b2e8448..c5c20673b5b5b70fa41516b9ba4a399eb9d4ce80 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -3386,6 +3386,16 @@
         ],
       },
     }],
+    ['OS=="linux" and target_arch=="arm" and host_arch!="arm" and chromeos==0 and clang==0', {
+      # Some sensible defaults for ARM cross compiling on linux.  These can be overridden

[Mark Seaborn, 2014/07/28 15:55:20]

Line is >80 chars

[Sam Clegg, 2014/07/29 00:28:11]

There are other occurrences of conditions in this file that overflow the 80 char
line so I assumed that was ok (line 110, line 211 for example).

+      # using CC/CXX/etc environment variables.
+      'make_global_settings': [
+        ['CC', '<!(which arm-linux-gnueabihf-gcc)'],

[Mark Seaborn, 2014/07/28 15:55:20]

The bot configs also set AR, AS and RANLIB (see
https://src.chromium.org/viewvc/chrome/trunk/tools/build/scripts/slave/recipe...).
 Are any of those necessary?

[Sam Clegg, 2014/07/29 00:28:11]

Apparently not.  Its hard to be 100% since there are C++11 issues that currently
make building with arm/gcc on precise impossible, but I can build many targets.

+        ['CXX', '<!(which arm-linux-gnueabihf-g++)'],
+        ['CC.host', '<!(which gcc)'],
+        ['CXX.host', '<!(which g++)'],
+      ],
+    }],
     ['os_posix==1 and OS!="mac" and OS!="ios"', {
       'target_defaults': {
         # Enable -Werror by default, but put it in a variable so it can