BaseTools/Scripts: discard .gnu.hash section in GCC builds

BaseTools/Scripts: discard .gnu.hash section in GCC builds

Some builds of GCC/binutils will default to using the GNU flavor of
the symbol hash table, and will emit it into a section called .gnu.hash
rather than .hash. We have no use for its contents, and GenFw ignores
it anyway, so it shouldn't really matter what we do with it.

However, due to a workaround for AARCH64 we have in GenFw to deal with
older GCCs that corrupt section-based relocations when merging sections
during the final link, we need the ELF and PE/COFF views of the binary
to be identical. Since we don't place the .gnu.hash section explicitly,
it may end up at the beginning of the ELF binary, causing other sections
to be shifted in the ELF view but not in the PE/COFF view.

So let's add .gnu.hash to the GCC linker script. We don't care about its
contents so add it to the /DISCARD/ section.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Tested-by: Leif Lindholm <leif.lindholm@linaro.org>
Reviewed-by: Liming Gao <liming.gao@intel.com>