This targets all 32-bit platforms and windows.
The test for off_t == off64_t from D4167 is updated to accommodate OSX
not providing the off64_t type and renamed to be more meaningful as a
check for LFS.
The -D_FILE_OFFSET_BITS=64 is added to enable LFS, which is the
correct flag for all our currently supported platforms. Other flags can
be added later for other platforms as needed. Note that mingw also
requires a linker flag for win32.
Depends on D4167.