libffi: Backport of LoongArch support for libffi.

libffi: Backport of LoongArch support for libffi.

This is a backport of <https://github.com/libffi/libffi/commit/f259a6f6de>,
and contains modifications to commit 5a4774cd4d, as well as the LoongArch
schema portion of commit ee22ecbd11. This is needed for libgo.

libffi/ChangeLog:

	PR libffi/108682
	* configure.host: Add LoongArch support.
	* Makefile.am: Likewise.
	* Makefile.in: Regenerate.
	* src/loongarch64/ffi.c: New file.
	* src/loongarch64/ffitarget.h: New file.
	* src/loongarch64/sysv.S: New file.