[nvptx] Fix 'main (int argc)' compilation

[nvptx] Fix 'main (int argc)' compilation

On nvptx, with test-case sso-12.c I run into:
...
spawn nvptx-none-run ./sso-12.exe^M
error: Prototype doesn't match for 'main' in 'input file 1 at offset 1796', \
  first defined in 'input file 1 at offset 1796'^M
nvptx-run: cuLinkAddData failed: device kernel image is invalid \
  (CUDA_ERROR_INVALID_SOURCE, 300)^M
FAIL: gcc.dg/sso-12.c execution test
...

The problem is that the test case uses 'main (int)' prototype, while __main
uses:
...
extern int main (int, void **);
...

There's code in write_fn_proto_1 to handle 'main (void)' as if
'main (int, void **)' was specified, but that's not active for 'main (int)'.

Fix this in write_fn_proto_1 by handling 'main (int)' as if
'main (int, void **)' was specified.

Tested on nvptx.

gcc/ChangeLog:

2022-02-07  Tom de Vries  <tdevries@suse.de>

	* config/nvptx/nvptx.cc (write_fn_proto_1): Handle 'main (int)'.