Add -Wsign-compare for C++ compilation on linux & friends.

Add -Wsign-compare for C++ compilation on linux & friends.
g++ -Wall includes -Wsign-compare on C++ source, but clang++ doesn't.

(this is a 2nd attempt to land this change, after 79846 had to be rolled back
because clang's -Wsign-compare semantics were different from gcc's; this has
been fixed in clang 135664)

BUG=none
TEST=chrome builds w/ rolled clang, trybots

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=93837

[Evan Martin, 2011-07-22 23:25:54]

LGTM, I guess -- but what is the benefit?  are you looking for better coverage
on clang?

[Ami GONE FROM CHROMIUM, 2011-07-22 23:29:09]

On 2011/07/22 23:25:54, Evan Martin wrote:
> LGTM, I guess -- but what is the benefit?  are you looking for better coverage
> on clang?

Without this change, people who build w/ clang on their desktops only find out
about violations of -Wsign-compare at trybot (or, horror!, buildbot) time.
With this change, those same people will see their violations at local-compile
time.

[Nico, 2011-07-22 23:43:58]

(other than that lgtm)

http://codereview.chromium.org/7493029/diff/2001/build/common.gypi
File build/common.gypi (right):

http://codereview.chromium.org/7493029/diff/2001/build/common.gypi#newcode1221
build/common.gypi:1221: # TODO(fischman): remove this if http://b/4187267
obsoletes it.
Please no links to internal bugs in public code. File a public shadow bug.

[Nico, 2011-07-22 23:46:51]

On 2011/07/22 23:43:58, Nico wrote:
> (other than that lgtm)
> 
> http://codereview.chromium.org/7493029/diff/2001/build/common.gypi
> File build/common.gypi (right):
> 
> http://codereview.chromium.org/7493029/diff/2001/build/common.gypi#newcode1221
> build/common.gypi:1221: # TODO(fischman): remove this if http://b/4187267
> obsoletes it.
> Please no links to internal bugs in public code. File a public shadow bug.

Ideally on the clang but tracker, I guess.

[Ami GONE FROM CHROMIUM, 2011-07-23 00:11:59]

On 2011/07/22 23:46:51, Nico wrote:
> On 2011/07/22 23:43:58, Nico wrote:
> > (other than that lgtm)
> > 
> > http://codereview.chromium.org/7493029/diff/2001/build/common.gypi
> > File build/common.gypi (right):
> > 
> >
http://codereview.chromium.org/7493029/diff/2001/build/common.gypi#newcode1221
> > build/common.gypi:1221: # TODO(fischman): remove this if http://b/4187267
> > obsoletes it.
> > Please no links to internal bugs in public code. File a public shadow bug.
> 
> Ideally on the clang but tracker, I guess.

Done.