pragma: use the directives hash to look up directive names

pragma: use the directives hash to look up directive names

Very few things have any desire to do its own string parsing, and the
directives hash is already a plain string-to-numbers O(1) hash.  The
namespace is small enough that even if it makes some switch statements
compile a bit larger there is no real reason to have separate hashes,
even if the actual code as opposed to the data structure was shared.

So, for right now, just throw them together in one big happy pot.

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