Fixes for testsuite failures introduced by the changes made for PR 19011.

Fixes for testsuite failures introduced by the changes made for PR 19011.

	PR19011
bfd	* cofflink.c (_bfd_coff_generic_relocate_section): Provide a value
	for undefined symbols which will not generate extra warning
	messages about truncated relocs.

ld	* testsuite/lib/ld-lib.exp (ld_link_defsyms): For PE based targets
	define the __main and ___main symbols in terms of the main symbol.