fix x32 handling of Atomic64

The x32 logic for the size of Atomic64 handles NaCL, but misses
the Linux case.  Check the standard __ILP32__ to handle that too.

This has been fixed in the Chromium base tree already:
https://codereview.chromium.org/12186005/

BUG=chromium-os:36866
TEST=compiled the code for x86_64 (64bit) & x86_64 (x32)

Review URL: https://codereview.chromium.org/12374065
Patch from Mike Frysinger <vapier@chromium.org>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@13824 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/atomicops.h

@@ -58,7 +58,7 @@ typedef int32_t Atomic32;
 #ifdef V8_HOST_ARCH_64_BIT
 // We need to be able to go between Atomic64 and AtomicWord implicitly.  This
 // means Atomic64 and AtomicWord should be the same type on 64-bit.
-#if defined(__APPLE__)
+#if defined(__ILP32__) || defined(__APPLE__)
 // MacOS is an exception to the implicit conversion rule above,
 // because it uses long for intptr_t.
 typedef int64_t Atomic64;