Improve x32 detection macro.

Improve x32 detection macro.

When targeting the Microsoft ABI in 64bit mode, clang defines __x86_64__ but
doesn't define __LP64__ (Microsoft uses LLP64), so it would fall down the x32
path. cl.exe doesn't define __x86_64__ in the first place, so it didn't have
this problem.

Rather than trying to guess pointer size by looking at __x86_64__ and __LP64__,
check for pointer size directly using __POINTER_SIZE__. This is defined by both
gcc and clang, and eliminiates this problem.

This should fix hundreds of "error(clang): unknown type name 'Atomic64'" when
compiling v8 on Windows with clang for 64 bit.

BUG=chromium:82385
LOG=n
R=haitao.feng@intel.com, jochen@chromium.org

Committed: https://code.google.com/p/v8/source/detail?r=23855

[Nico, 2014-09-10 17:56:25]

thakis@chromium.org changed reviewers:
+ jochen@chromium.org

[Nico, 2014-09-10 17:56:26]

(see also http://llvm.org/PR20896)

[Nico, 2014-09-10 17:58:21]

(from the llvm bug: https://sourceware.org/glibc/wiki/x32 recommends to check
__ILP32__ instead, no idea if that's better or any different in practice from
what this patch does.)

[hans, 2014-09-10 18:05:44]

hans@chromium.org changed reviewers:
+ hans@chromium.org

[hans, 2014-09-10 18:05:44]

https://codereview.chromium.org/560903002/diff/1/src/base/build_config.h
File src/base/build_config.h (right):

https://codereview.chromium.org/560903002/diff/1/src/base/build_config.h#newc...
src/base/build_config.h:27: #if defined(__x86_64__) && __SIZEOF_POINTER__ == 32 
// Check for x32.
I don't think __SIZEOF_POINTER__ is in bits.

[Nico, 2014-09-10 18:08:20]

https://codereview.chromium.org/560903002/diff/1/src/base/build_config.h
File src/base/build_config.h (right):

https://codereview.chromium.org/560903002/diff/1/src/base/build_config.h#newc...
src/base/build_config.h:27: #if defined(__x86_64__) && __SIZEOF_POINTER__ == 32 
// Check for x32.
On 2014/09/10 18:05:44, hans wrote:
> I don't think __SIZEOF_POINTER__ is in bits.

Done.

[haitao.feng, 2014-09-11 01:24:21]

LGTM

[jochen (gone - plz use gerrit), 2014-09-11 08:00:24]

jochen@chromium.org changed reviewers:
+ haitao.feng@intel.com

[jochen (gone - plz use gerrit), 2014-09-11 08:00:25]

lgtm

[jochen (gone - plz use gerrit), 2014-09-11 08:01:32]

Committed patchset #2 (id:20001) manually as 23855 (presubmit successful).