Intent to fix windows not compiling after r53480.

Looks like _Bool is also a type in std (at least with msvc), so the 'typdef bool _Bool;' generates a name collision... Now using _BLI_Bool as placeholder instead.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@53488 954f8c5b-7b00-dc11-b283-0030488c597c