doc/Makefile.in: avoid deleting opt_var.txt, fix dependencies
doc/Makefile.in: avoid deleting opt_var.txt, fix dependencies

Fix dependencies in the generation of the instruction list, and make
sure we don't delete opt_var.txt on "make spotless".

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