Autodetect no-strict-aliasing, propagate toolchain option to SCons

Autodetect no-strict-aliasing, propagate toolchain option to SCons

Patch by Bert Belder.

BUG=v8:884
Committed: http://code.google.com/p/v8/source/detail?r=7449

[piscisaureus, 2011-02-17 04:00:32]

- Compiling with GCC 4.5.x produces a nonfunctional v8; this is fixed by
checking for gcc 4.5.x, and if it is found adding the -fno-strict-aliasing flag.

- The selected toolchain is not properly propagated to SCons, so when
toolchain=gcc is selected on a machine that also has msvc installed, it fails.

[piscisaureus, 2011-03-16 10:38:51]

Minor fix to detect gcc 4.5.0, for which `gcc -dumpversion` apparently reports
just '4.5'.

Rebased the patch set.

[Vyacheslav Egorov (Chromium), 2011-03-29 11:59:33]

http://codereview.chromium.org/6539006/diff/2001/SConstruct
File SConstruct (right):

http://codereview.chromium.org/6539006/diff/2001/SConstruct#newcode696
SConstruct:696: version = subprocess.Popen([env['CC'], '-dumpversion'],
should not we just rely on env['CCVERSION'] instead of guessing it manually?

http://codereview.chromium.org/6539006/diff/2001/SConstruct#newcode872
SConstruct:872: while len(options):
Seems a bit too complicated for the current use case where a couple of options
depends on the os & toolchain.

I think simpler is just to split SIMPLE_OPTIONS into two parts. os, toolchain
(and maybe arch) will be in one part and everything else will be in the other
part.

[piscisaureus, 2011-03-29 15:50:40]

- Split up the options list instead of adding dependency resolution.
- Added a comment justifying not relying on env['CCVERSION']

[Vyacheslav Egorov (Chromium), 2011-03-30 17:18:24]

LGTM,

will land.

Thanks for fixing this Bert!