Post-release version bump to 0.28.1
Fix undeclared variable use and sysctlbyname error handling on ppc

Fixes bug 56889.
Always use xmmintrin.h for 64 bit Windows

MinGW-w64 uses the GNU compiler and does not define _MSC_VER.
Nevertheless, it provides xmmintrin.h and must be handled
here like the MS compiler. Otherwise compilation fails due to
conflicting declarations.

Signed-off-by: Stefan Weil <sw@weilnetz.de>
Fix thread safety on mingw-w64 and clang

After finding a working TLS storage class specifier, configure was
continuing to test other candidates.  This caused it to prefer
__declspec(thread) over __thread.  However, __declspec(thread) is
ignored with a warning by mingw-w64 [1] and silently ignored by clang [2].
The resulting binary behaved as if PIXMAN_NO_TLS was defined.

Bug introduced by a069da6c.

[1] https://bugs.freedesktop.org/show_bug.cgi?id=57591
[2] http://lists.freedesktop.org/archives/pixman/2012-October/002320.html
Pre-release version bump to 0.28.2