nasm.h: move "regs.h" to top; make is_register() a bool
nasm.h: move "regs.h" to top; make is_register() a bool

Move the #include of regs.h to the top with the other includes, and
make is_register() -- being a boolean predicate -- return bool.

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

turingstudio/nasm,techkey/nasm,projedi/nasm,letolabs/nasm,turingstudio/nasm,letolabs/nasm,Distrotech/nasm,projedi/nasm,techkey/nasm,letolabs/nasm,turingstudio/nasm,techkey/nasm,projedi/nasm,Distrotech/nasm,Distrotech/nasm,Distrotech/nasm,techkey/nasm,turingstudio/nasm,projedi/nasm,techkey/nasm,projedi/nasm