PR modula2/126911: Tidyup removing files

This tiny patch tidies up the removal of a file using
a function testing for the name being not None and that it exists.
Boostrapped on Debian x86_64.

gcc/m2/ChangeLog:

	PR modula2/126911
	* tools-src/mktargetsrc.py (safeRemove): New function.
	(quietSystem): Call safeRemove for temporaryFile and
	args.outputfile.

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