[ELF] - Don't segfault when assigning non-calculatable absolute symbol value.

This is PR32664.

Issue was revealed by linux kernel script which was:

SECTIONS {
 . = (0xffffffff80000000 + ALIGN(0x1000000, 0x200000));
 phys_startup_64 = ABSOLUTE(startup_64 - 0xffffffff80000000);

 .text : AT(ADDR(.text) - 0xffffffff80000000) {
.....
  *(.head.text)
Where startup_64 is in .head.text.

At the place of assignment to phys_startup_64 we can not calculate absolute value for startup_64
because .text section has no VA assigned. Two patches were prepared earlier to address this: D32173 and D32174.

And in comments for D32173 was suggested not try to support this case, but error out.

Differential revision: https://reviews.llvm.org/D32793

llvm-svn: 302668