Tidy up to declarations allowing files to be built by gm2

Tidy up to declarations allowing files to be built by gm2

This patch adds missing declarations in export qualified lists
and fixes comparisons of an address type against NIL.
These changes allow make m2/stage2/cc1gm2 to succeed when in
maintainer mode.

gcc/m2/ChangeLog:

	* gm2-compiler/M2Options.def: Export GetMQ, SetMQ.
	* gm2-compiler/M2Preprocess.mod: (MakeSaveTempsFileName):
	Test NewDir against NIL.  Test Dumpdir against NIL.
	Test GetMD () against NIL.  Test GetMMD () against NIL.
	Test GetMQ () against NIL.  Test GetObj () against NIL.
	Test tempfile against NIL.
	* gm2-compiler/P2SymBuild.def: Export
	BuildNoReturnAttribute.

Signed-off-by: Gaius Mulley <gaiusmod2@gmail.com>