[nvptx] Replace dots in function names

[nvptx] Replace dots in function names

When function splitting clones a function sinf in the host compiler, the clone
is callled sinf.part.0.  However, ptx does not allows dots in identifiers, so
we run into:
...
ptxas test.o, line 23; fatal   : Parsing error near '.part': syntax error
ptxas fatal   : Ptx assembly aborted due to errors
nvptx-as: ptxas returned 255 exit status
...

Rename such functions by replacing the dots with dollar signs.

Tested check-gcc on nvptx.

Tested libgomp on x86_64-linux with nvptx accelerator.

gcc/ChangeLog:

2020-10-10  Tom de Vries  <tdevries@suse.de>

	PR target/97318
	* config/nvptx/nvptx.c (nvptx_replace_dot): New function.
	(write_fn_proto, write_fn_proto_from_insn, nvptx_output_call_insn):
	Use nvptx_replace_dot.