ld/testing: run_dump_test can now check linker mapfiles.

ld/testing: run_dump_test can now check linker mapfiles.

Add a new option 'map' to the ld run_dump_test mechanism.  When the
'map' option is given run_dump_test will ensure that there is a
-Map=MAPFILE present in the linker command line, adding one if needed.

The MAPFILE is then compared with the file passed to the new 'map'
option using the regexp_diff function.  This should make it slightly
easier to write tests that check the linker mapfile output.

The only test I found that already compares mapfile content is updated
to use the new mechanism.

ld/testsuite/ChangeLog:

	* ld-scripts/overlay-size.d: Add 'map' option.
	* ld-scripts/overlay-size.exp: Remove manual check of mapfile.
	* lib/ld-lib.exp (run_dump_test): Add support for new 'map'
	option, checking linker mapfile output.