tools/gengetopt: override SUBDIRS variable with Makefile

tools/gengetopt: override SUBDIRS variable with Makefile

Instead of editing the SUBDIRS variable with a patch,
it can be overriden at the end of the command line when invoking Make.

This tool has a series of recursive Makefiles in each subdirectory,
therefore SUBDIRS is set to a pattern of Make functions
so that the result is variable depending on the current subdirectory
that Make is being invoked in.

By eliminating the patch, autoreconf is no longer required.

Signed-off-by: Michael Pratt <mcpratt@pm.me>