Support Cygwin, MinGW, VS2012.

For Cygwin, update gcc, g++, stdlibc++ to v4.7.2 and install svn, cmake
then enable pthreads in gtest.
For MinGW, install apache subversion command line tools
(http://www.visualsvn.com/downloads/), generate MSYS Makefiles using
CMake-GUI and disable pthreads in gtest. (Note: MinGW doesn't provide
Linux or Unix system calls or a POSIX emulation layer)
For VS2012, set _VARIADIC_MAX=10, choose STLPort or not.
NOTE: not support -std=c++11 on Cygwin and MinGW.