[asan] Allow -fsanitize-address-globals-dead-stripping with -fno-data-sections for ELF

-fdata-sections decides whether global variables go into different sections.
This is orthogonal to whether we place their metadata (`.data` or `asan_globals`) into different sections.

With -fno-data-sections, `-fsanitize-address-globals-dead-stripping` can still:

* deduplicate COMDAT `asan.module_ctor` and `asan.module_dtor`
* (with ld --gc-sections): for a data section (e.g. `.data`), if all global variables defined relative to it are unreferenced, discard them and associated `asan_globals` sections (rare but no need to exclude this case)

Similar to c7b90947 for PE/COFF.

Reviewed By: #sanitizers, kstoimenov, vitalybuka

Differential Revision: https://reviews.llvm.org/D120394