nvptx: Emit DECL and DEF linker markers for aliases [PR104957]

nvptx: Emit DECL and DEF linker markers for aliases [PR104957]

With nvptx '-malias' enabled (as implemented in
commit f8b15e177155960017ac0c5daef8780d1127f91c
"[nvptx] Use .alias directive for mptx >= 6.3"), the C++ front end in certain
cases does 'write_fn_proto' before an eventual 'alias' attribute has been
added.  In that case, we do emit (via 'write_fn_marker') a DECL linker marker,
but then never emit a corresponding DEF linker marker for the alias.  This
causes hundreds of instances of link-time 'unresolved symbol [alias]' across
the C++ test suite, which are regressions compared to a test run with (default)
'-mno-alias' (in which case the respective functions get duplicated).

	PR target/104957
	gcc/
	* config/nvptx/nvptx.cc (write_fn_proto_1): Revert 2022-03-22
	change; 'write_fn_marker' also for alias DECL.
	(nvptx_asm_output_def_from_decls): 'write_fn_marker' for alias
	DEF.
	gcc/testsuite/
	* g++.target/nvptx/alias-g++.dg_init_dtor2-1.C: Un-XFAIL.
	* gcc.target/nvptx/alias-1.c: Likewise.
	* gcc.target/nvptx/alias-3.c: Likewise.
	* gcc.target/nvptx/alias-to-alias-1.c: Likewise.