This fixes building on mingw-w64.
Include stdint.h on everything except MSVC for definitions of
common standard types, include stddef.h on MSVC instead, since
MSVC doesn't have stdint.h in all older versions that are
supposed to be supported, but MSVC always defines intptr_t via
stddef.h.
The old InitializeCriticalSection function isn't available in
these API partitions, and the new InitializeCriticalSectionEx
function is only available since Vista, so we want to keep using
the old function for normal desktop code.
astyle was only run on .cpp files this time - already in
ff6b66917 where the style cleanup was done initially, not all
.h files seem to have gotten the same styling (rerunning astyle
on .h files at that commit produces a huge diff).
