PE/Windows x86_64: Fix weak undef symbols after image base change

PE/Windows x86_64: Fix weak undef symbols after image base change

The change in PR19011 changed the image load address from being in the lower
32-bit address space to the higher 64-bit address space.

However when you have a weak undef symbol which stays undef at the end of
linking the linker has to resolve this (Windows loader does not support undef
symbols).  As such typically these would resolve to 0.

The relocation used for these weak symbols are the normal 32-bit PC_REL call
relocs.  So when doing the overflow check LD checks if the distance between the
symbol and the call is within range.  However now that the load address is
> 32-bits and the symbol val is 0 this overflow check will always fail.

As such the linker gives a bogus error.  This patch makes the linker not emit
the overflow failure but chooses to still let the check be performed (as it's
mid-end code).

One down side of this is that it does break the common convention that the call
be to sym at 0x0. i.e. before you'd get

      401015:   74 05                   je     40101c
      401017:   e8 e4 ef bf ff          callq  0

and now you get

   140001015:   74 05                   je     14000101c
   140001017:   e8 e4 ef ff bf          call   100000000

since the call is PC_REL there's no way to get the range large enough to
resolve to 0.  As such I have chosen to leave it as the furthest simple range
that we can still represent.

By only ignoring the error we leave the symbol value itself to still be 0
such that the if(<symbol>) checks still work correctly.

bfd/ChangeLog:

2021-04-01  Tamar Christina  <tamar.christina@arm.com>

	PR ld/26659
	* cofflink.c (_bfd_coff_generic_relocate_section): Ignore overflow.

ld/ChangeLog:

2021-04-01  Tamar Christina  <tamar.christina@arm.com>

	PR ld/26659
	* testsuite/ld-pe/pe.exp: Add test.
	* testsuite/ld-pe/pr26659-weak-undef-sym.d: New test.
	* testsuite/ld-pe/pr26659-weak-undef-sym.s: New test.