Move bittest* functions from winnt.h to intrin-impl.h

1) Move these functions from winnt.h to intrin-impl.h:

_bittest, _bittest64
_bittestandset, _bittestandreset, _bittestandcomplement
_bittestandset64, _bittestandreset64, _bittestandcomplement64

2) Update inline asm code:

a) Remove "memory" clobber.
b) Remove volatile keyword.
c) Several changes to inputs, outputs, constraints and clobbers.
d) Use macros & symbolic names.
e) Support both att and intel asm formats.

git-svn-id: svn://svn.code.sf.net/p/mingw-w64/code/trunk@5986 4407c894-4637-0410-b4f5-ada5f102cad1