Allow __pnacl__ target to build code included from Chrome.

Committing for pdox@google.com.
BUG=none
TEST=trybots

Review URL: http://codereview.chromium.org/7744034

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@98461 0039d316-1c4b-4281-b951-d872f2087c98

build/build_config.h

@@ -110,6 +110,8 @@
 #define ARCH_CPU_32_BITS 1
 #define ARCH_CPU_LITTLE_ENDIAN 1
 #define WCHAR_T_IS_UNSIGNED 1
+#elif defined(__pnacl__)
+#define ARCH_CPU_32_BITS 1
 #else
 #error Please add support for your architecture in build/build_config.h
 #endif