ld: fix coff PE SEH

COFF_WITH_pex64 and COFF_WITH_peAArch64 can't be true at the same time.
That means that two conditionals that control the sorting of the .pdata section
became a falsum.

The testsuite doesn't catch this because the linker does the sorting and to link
you require library support from the unwinder so we can't test from binutils in
isolation.

bfd/ChangeLog:

2021-12-31  Tamar Christina  <tamar.christina@arm.com>

	PR ld/28682
	* peXXigen.c: Fix conditional.