Default to parallel gyp on non-win platforms

Setting GYP_PARALLEL=0 on posix will turn off parallel gyp.

BUG=chromium:154205
R=dmazzoni@chromium.org, thakis@chromium.org

Review URL: https://codereview.chromium.org/18603014

git-svn-id: http://gyp.googlecode.com/svn/trunk@1666 78cadc50-ecff-11dd-a971-7dbc132099af
Make root invocation less crazy so that multiprocessing works on Windows

Previously gyp.bat runs "python gyp" and "gyp" imports "gyp" expecting to
get pylib/gyp/__init__.py. Multiprocessing tries to fork and doesn't find
the entry point named gyp because it doesn't search for non-.py
extensions.

Instead, make non-Windows match with a wrapper 'gyp' in bash, and make the
python entry point gyp_main.py so that importing works more normally.

Also, remove "Using parallel processing..." message so that tests pass,
otherwise they complain that there was output on stderr. This was failing
on other OSs too.

R=thakis@chromium.org
BUG=154205

Review URL: https://codereview.chromium.org/18271010

git-svn-id: http://gyp.googlecode.com/svn/trunk@1667 78cadc50-ecff-11dd-a971-7dbc132099af
Fix fake assembler on vs2012

(causing tests to fail currently)

TBR=bradnelson@google.com

Review URL: https://codereview.chromium.org/18500016

git-svn-id: http://gyp.googlecode.com/svn/trunk@1668 78cadc50-ecff-11dd-a971-7dbc132099af