Fix t-locale.c #define used to avoid a test when using mingw64

The macro __MINGW64_VERSION_MAJOR is defined even when mingw64 is being used to compile 32 bit versions of software with the -m32 switch.

__MINGW64__ is only defined while compiling 64 bit output.
Update Visual Studio 2012 builds and simply tune builds for VS2012 and VS2013
Merge branch 'master' of https://github.com/wbhart/mpir
correct C++ assign test
Added atom tuning values. Thanks Jason Preszler.
Add missing fat tuning values.
Fixed an aliasing bug in nthroot.
Added tuning values for IvyBridge.
Added test case for nthroot aliasing and fixed code.
Update tuning values for x86_64w/fat.
Attempt to fix fat build on MinGW64.
Merge remote-tracking branch 'brian/master'

Conflicts:
	tests/cxx/t-assign.cc
Whoops, we defined GMP_CC twice.
Experiment with correct size_t format specifier.
tuning plus cosmetic change to mpir_config.py
Attempt to fix some compiler warnings on MinGW64.
Merge branch 'master' of https://github.com/wbhart/mpir
update all Visual Studio builds for latest name changes
Handle stdint detection differently and fix a typo in README (thanks Dann
Corbit)
Merge remote-tracking branch 'brian/master'