Make gtest always use simple internal regex engine.

In order to allow regex matches in gtest to be shared between Windows and other
systems, we tell gtest to always use it's internal engine.

The syntax supported by the internal engine initially looks like a subset of
POSIX regexs. However character class shortcuts are not valid POSIX.

Even more confusingly the system POSIX regex function often defines extra
features not actually part of the standard allowing regex that work on Linux
fail on Mac OS X.

A search through the code base did not reveal any locations where features not
supported by the internal regex engine where used.

See bug https://code.google.com/p/chromium/issues/detail?id=317224 for more detailed description.

BUG=317224

Review URL: https://codereview.chromium.org/55983002

git-svn-id: http://src.chromium.org/chrome/trunk/src/testing@239423 4ff67af0-8c30-449e-8e8b-ad334ec8d88c