Add an cross include path for ARM to work around clang bug 22937.

pydir/targets.py

 #!/usr/bin/env python2
 
 from collections import namedtuple
+import glob
+
+
+# Why have 'cross_headers':
+# For some reason, clang doesn't know how to find some of the libstdc++
+# headers (c++config.h). Manually add in one of the paths:
+# https://llvm.org/bugs/show_bug.cgi?id=22937
+# Otherwise, we could assume the system has arm-linux-gnueabihf-g++ and
+# use that instead of clang, but so far we've just been using clang for
+# the unsandboxed build.
+def FindARMCrossInclude():
+  return glob.glob(
+      '/usr/arm-linux-gnueabihf/include/c++/*/arm-linux-gnueabihf')[-1]
+
 
 TargetInfo = namedtuple('TargetInfo',
-                        ['target', 'triple', 'llc_flags', 'ld_emu'])
+                        ['target', 'triple', 'llc_flags', 'ld_emu',
+                         'cross_headers'])
 
 X8632Target = TargetInfo(target='x8632',
                          triple='i686-none-linux',
                          llc_flags=['-mcpu=pentium4m'],
-                         ld_emu='elf_i386_nacl')
+                         ld_emu='elf_i386_nacl',
+                         cross_headers=[])
 
 X8664Target = TargetInfo(target='x8664',
                          triple='x86_64-none-linux',
                          llc_flags=['-mcpu=x86-64'],
-                         ld_emu='elf_x86_64_nacl')
+                         ld_emu='elf_x86_64_nacl',
+                         cross_headers=[])
 
 ARM32Target = TargetInfo(target='arm32',
                          triple='armv7a-none-linux-gnueabihf',
                          llc_flags=['-mcpu=cortex-a9',
                                     '-float-abi=hard',
                                     '-mattr=+neon'],
-                         ld_emu='armelf_nacl')
+                         ld_emu='armelf_nacl',
+                         cross_headers=['-isystem', FindARMCrossInclude()])
 
 
 def ConvertTripleToNaCl(nonsfi_triple):
   return nonsfi_triple.replace('linux', 'nacl')