Refs #281. Detect _WIN32 macro for Windows API.

http://www.mail-archive.com/bug-gnulib@gnu.org/msg05722.html
Refs #281. Detect __CYGWIN__ macro for Cygwin x86_64.

Signed-off-by: Zhang Xianyi <traits.zhang@gmail.com>
Merge branch 'bulldozer' into develop
Avoid failure on qemu guests declaring an Athlon CPU without 3dnow!

The present patch verifies that, on machines declaring an Athlon CPU model and
family, the 3dnow and 3dnowext feature flags are indeed present. If they are
not, it fallbacks on the most generic x86 kernel. This prevents crashes due to
illegal instruction on qemu guests with a weird configuration.

Closes #272
Merge pull request #288 from sebastien-villemot/develop

Avoid failure on qemu guests declaring an Athlon CPU without 3dnow!
get rid of the generated cblas_noconst.h file
fix default prefix handling in makefiles

PREFIX wasn't communicated to Makefile.install (where it matters)
by Makefile. The result is that the default PREFIX is empty and
OpenBLAS was being installed in /lib.
Merge pull request #289 from larsmans/no-noconst

get rid of the generated cblas_noconst.h file
Merge pull request #291 from larsmans/fix-makefile-prefix

fix default prefix handling in makefiles
Merge pull request #290 from larsmans/missing-threshold

check if GEMM_MULTITHREAD_THRESHOLD defined in gemm.c
Set a fallback value.
Added backers.
Refs #262. Fixed compatibility issues of GNU stack markings with PathScale EKOPath(tm) Compiler Suite: Version 4.0.12.1
Merge remote branch 'origin/develop' into bulldozer