nasmlib/path.c: a few more detection macros
nasmlib/path.c: a few more detection macros

Add a few more operating system detection macros, including BeOS.

Signed-off-by: H. Peter Anvin <8a453bad9912ffe59bc0f0b8abe03df9be19379e@zytor.com>

techkey/nasm,techkey/nasm,techkey/nasm,techkey/nasm,techkey/nasm