BTF: fix PR debug/112656

BTF: fix PR debug/112656

PR debug/112656 - btf: function prototypes generated with name

With this patch, all BTF_KIND_FUNC_PROTO will appear anonymous in the
generated BTF section.

As noted in the discussion in the bugzilla, the number of
BTF_KIND_FUNC_PROTO types output varies across targets (BPF with -mco-re
vs non-BPF targets).  Hence the check in the test case merely checks
that all BTF_KIND_FUNC_PROTO appear anonymous.

gcc/ChangeLog:

	PR debug/112656
	* btfout.cc (btf_asm_type): Fixup ctti_name for all
	BTF types of kind BTF_KIND_FUNC_PROTO.

gcc/testsuite/ChangeLog:

	PR debug/112656
	* gcc.dg/debug/btf/btf-function-7.c: New test.