[JITLink][ELF][AArch64] Add support for ELF R_AARCH64_ABS32 relocation.

This relocation is commonly used in debug sections. Failure to handle it caused
the test failure in https://lab.llvm.org/buildbot/#/builders/197/builds/4272,
which forced the reversion, in f721fcb6, of 57aeb305 ("[JITLink][ELF]
Don't skip debug info sections by default"). This fix should allow us to
re-land 57aeb305.