Couple of minor tweaks to the linker testsuite.

Couple of minor tweaks to the linker testsuite.

This gets rid of the couple of linker failures for visium-elf:

FAIL: ld-elf/pr14156b
FAIL: ld-elf/pr22677

by tweaking the respective testcases.  The first tweak is the same as the
one made to the sibling testcase ld-elf/pr14156a.d about one year ago and
the  second tweak adds the usual main/start/_start/__start symbols.

ld/
	* testsuite/ld-elf/pr14156b.d: Adjust for extra symbols.
	* testsuite/ld-elf/pr22677.s: Define main/start/_start/__start.