Do not define POSIX.

It breaks integration with upstream re2 library on Chromium.

Without patching re2 library, with this define, it produces the
following error:

../../third_party/re2/re2/re2.h:254:5: error: expected identifier
    POSIX, // POSIX syntax, leftmost-longest match

As we define POSIX on the command line, the C preprocessor changes
RE2::POSIX to nothing and thus break the compilation. :(

See chromium-dev mailing list for this discussion in
https://groups.google.com/a/chromium.org/d/topic/chromium-dev/UXCHnX7pV44/discussion

BUG=None
TEST=ninja -C out/Debug, everything compiles as before
R=sergeyu@chromium.org, tommi@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/46049004

Patch from Thiago Farina <tfarina@chromium.org>.

Cr-Original-Commit-Position: refs/heads/master@{#9032}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 91543731c3a850dcc52ae63be8cc257e507fb72d
1 file changed