BaseTools: aarch64: add -fno-asynchronous-unwind-tables to gcc cflags

BaseTools: aarch64: add -fno-asynchronous-unwind-tables to gcc cflags

Some toolchains, at least Fedora GCC, generate inline unwind tables in
object files. These confuses GenFw to no end, leading to build failures:
  GenFw: ERROR 3000: Invalid WriteSections64(): ...
         unsupported ELF EM_AARCH64 relocation 0x105.
  GenFw: ERROR 3000: Invalid WriteSections64(): ...
         unsupported ELF EM_AARCH64 relocation 0x0.

I am aware of no current use of these tables, so explicitly disable
their generation for aarch64.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Leif Lindholm <leif.lindholm@linaro.org>
Tested-by: Wei Huang <wei@redhat.com>
Reviewed-by: Olivier Martin <olivier.martin@arm.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@17905 6f19259b-4bc3-4df7-8a09-765794883524