[nvptx] Improve help description of misa and mptx

Currently we have:
...
$ gcc --target-help 2>&1 | egrep "misa|mptx"
  -misa=                      Specify the version of the ptx ISA to use.
  -mptx=                      Specify the version of the ptx version to use.
  Known PTX ISA versions (for use with the -misa= option):
  Known PTX versions (for use with the -mptx= option):
...

As reported in PR104818, the "version of the ptx version" doesn't make much
sense.

Furthermore, the description of misa (and 'Known ISA versions') is misleading
because it does not specify the version of the PTX ISA, but rather the PTX ISA
target architecture.

Fix this by printing instead:
...
$ gcc --target-help 2>&1 | egrep "misa|mptx"
  -misa=                      Specify the PTX ISA target architecture to use.
  -mptx=                      Specify the PTX ISA version to use.
  Known PTX ISA target architectures (for use with the -misa= option):
  Known PTX ISA versions (for use with the -mptx= option):
...

Tested on nvptx.

gcc/ChangeLog:

2022-03-28  Tom de Vries  <tdevries@suse.de>

	PR target/104818
	* config/nvptx/gen-opt.sh (ptx_isa): Improve help text.
	* config/nvptx/nvptx-gen.opt: Regenerate.
	* config/nvptx/nvptx.opt (misa, mptx, ptx_version): Improve help text.
	* config/nvptx/t-nvptx (s-nvptx-gen-opt): Add missing dependency on
	gen-opt.sh.

0 files changed, 0 insertions, 0 deletions