Add {release,debug}_extra_cflags for mac and linux

There was already release_extra_cflags for linux;
this just generalizes it to debug_ and to mac.

Required a litle rearranging.  Tested by comparing
xcode and make files before and after change.

Ignores those settings when generating Visual C++ projects,
but since the goal was to let valgrind bots tweak
optimization settings, that's ok for now.

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=25997

[dank, 2009-09-11 17:26:52]

(Avoided adding new platform specific variables,
but didn't clean up any of the old ones.)

[Mark Mentovai, 2009-09-11 17:32:25]

lg otherwise

http://codereview.chromium.org/202054/diff/2001/3001
File build/common.gypi (right):

http://codereview.chromium.org/202054/diff/2001/3001#newcode171
Line 171: 'release_extra_cflags%':   '',
Don't put all of that extra space, we don't do that elsewhere.

http://codereview.chromium.org/202054/diff/2001/3001#newcode236
Line 236: 'OTHER_CFLAGS': '<(debug_extra_cflags)',
I think this should be ['<@(debug_extra_cflags)'] as is done for Linux.  Same
for release.

http://codereview.chromium.org/202054/diff/2001/3001#newcode263
Line 263: '<@(debug_extra_cflags)',
Indent is wrong.  Same for release.