Set V8_CC_GNU or V8_CC_MSVC for clang in gcc / cl mode.

Set V8_CC_GNU or V8_CC_MSVC for clang in gcc / cl mode.

Also, remove V8_CC_CLANG since it's not read anywhere (and ideally shouldn't
be).

Clang tries to be compatible with gcc in clang mode, and with msvc in clang-cl
mode. It wants to go down the same code paths that these compilers want to go
down in most cases.

For example, V8PRIxPTR was set incorrectly on Windows 64-bit before this change
since macros.h assumed that checking for V8_CC_MSVC is enough to find LLP64
systems, but V8_CC_MSVC wasn't set for clang.  Most other existing checks for
V8_CC_MSVC should be taken for clang-cl too (and for the remaining ones,
clang-cl is happy with either code path).

Likewise, V8_IMMEDIATE_CRASH is currently set to a suboptimal value with clang
since __builtin_trap() is only used if V8_CC_GNU is set.

Including clang in the gcc and cl macros is also what chromium does.

BUG=chromium:82385
LOG=y

[Nico, 2014-12-01 20:07:20]

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

[Nico, 2014-12-01 20:07:23]

Useful cs links:
https://code.google.com/p/chromium/codesearch#chromium/src/v8/include/v8confi...
https://code.google.com/p/chromium/codesearch#search/&q=v8_cc_gnu&sq=package:...
https://code.google.com/p/chromium/codesearch#search/&q=v8_cc_msvc&sq=package...

I think getting rid of the whole __clang__ block and conditionally setting a few
flags in the gcc block would be nice too, but one step at a time. (clang
masquerades as gcc 4.2, so most of the settings in the gcc block would already
be correct automatically.)

Unrelated questions I had while reading this file: Do you really support gccs as
old as 2.95? What's your minimum supported version? Do you intend to require
c++11 at some point?

[Benedikt Meurer, 2014-12-02 04:53:00]

Feel free to come up with a patch, but please try to do the changes in small
steps, and remember V8 is not Chromium-only, so there might always be some
corner cases that Chromium doesn't have to care about...

Currently we almost require C++11. Please talk to svenpanne@ about details wrt.
compiler versions/flags.

[Benedikt Meurer, 2014-12-02 04:54:12]

Argh, sorry, commenting on wrong CL, although that also applies here... :-)

LGTM

[Benedikt Meurer, 2014-12-02 04:54:17]

The CQ bit was checked by bmeurer@chromium.org

[commit-bot: I haz the power, 2014-12-02 04:54:54]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/757553004/1

[commit-bot: I haz the power, 2014-12-02 05:23:16]

Committed patchset #1 (id:1)