Fix for building ARM/linux using clang.

src/trusted/service_runtime/linux/nacl_bootstrap.gyp

 # Copyright (c) 2012 The Native Client Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 {
   'includes': [
     '../../../../build/common.gypi',
   ],
   'conditions': [
     ['target_arch=="x64"', {
@@ skipping 138 matching lines @@
             # set at gyp time. This is a hacky way to bake the correct
             # CXX into the build at gyp time.
             # TODO(sbc): Do this better by providing some gyp syntax
             # for accessing the name of the configured compiler, or
             # even a better way to access gyp time environment
             # variables from within a gyp file.
             ['OS=="android"', {
               'variables': {
                 'compiler': '<!(/bin/echo -n <(android_toolchain)/*-g++)',
               }
+            }],
+            # When building for ARM default to arm-linux-gnueabi-g++ rather
+            # than g++.  This is needed when building with clang (since in
+            # this case $CC and $CXX are not set in the envrionement).

[Mark Seaborn, 2014/07/28 19:23:20]

"environment"

+            ['OS!="android" and target_arch=="arm"', {
+              'variables': {
+                'compiler': '<!(echo ${CXX:=arm-linux-gnueabi-g++})',

[Roland McGrath, 2014/07/28 19:20:51]

I don't really understand what's going on here, but hard-coding this here seems
wrong.  It's as likely to be arm-linux-gnueabihf-g++, for example.

[Mark Seaborn, 2014/07/28 19:23:20]

It's a bit counterintuitive that in order to build with clang, you have to
specify arm-gcc here.

Would this then be the only place in the Gyp build where arm-gcc gets invoked? 
And would this be the only part that requires the arm-gcc Debian package to be
installed?

Is this only needed in conjunction with another change (like
https://codereview.chromium.org/414343003/)?

Could we get this to use the same host compiler that Gyp uses?  Is there any way
to refer to CC from 'make_global_settings'?  If not, could we add another
variable to common.gypi to define this compiler?

If this is tricky to resolve, I'd suggest sending the nacl_syscall_common.c
change as a separate change.

+              }
             }, {
               'variables': {
                 'compiler': '<!(echo ${CXX:=g++})',
               }
             }],
           ],
           'action': ['python', 'ld_bfd.py',
                      '--compiler', '<(compiler)',
                      '-m', '<(linker_emulation)',
                      '--build-id',
@@ skipping 35 matching lines @@
         'action_name': 'munge_phdr',
         'inputs': ['nacl_bootstrap_munge_phdr.py',
                    '<(PRODUCT_DIR)/nacl_bootstrap_raw'],
         'outputs': ['<(PRODUCT_DIR)/nacl_helper_bootstrap'],
         'message': 'Munging ELF program header',
         'action': ['python', '<@(_inputs)', '<@(_outputs)']
       }],
     },
   ],
 }