asm/nasm.c: Move directive parsing into a separate function

Move the directive parsing out of the main loop into a separate
function.  It is much cleaner this way, and opens up for further
refactoring -- a bunch of the directives do the same thing or very
similar things.

Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

asm/directiv.pl

@@ -45,7 +45,10 @@ require 'phash.ph';
 my($output, $directives_dat, $outfile) = @ARGV;
 
 @directives = ();
-@specials   = ('none', 'unknown');
+
+# Special values for enum directives.  Note that D_none must be first
+# so D_none == 0.
+@specials   = ('none', 'unknown', 'corrupt');
 
 open(DD, "< ${directives_dat}\0")
     or die "$0: cannot open: ${directives_dat}: $!\n";