[nvptx] Use --no-verify for sm_30

In PR97348, we ran into the problem that recent CUDA dropped support for
sm_30, which inhibited the build when building with CUDA bin in the path,
because the nvptx-tools assembler uses CUDA's ptxas to do ptx verification.

To fix this, in gcc-11 the default sm_xx was moved from sm_30 to sm_35.

This however broke support for sm_30 boards: an executable build for sm_30
might contain sm_35 code from the libraries, which are build with the default
sm_xx (PR104758).

We want to fix this by going back to having the libraries build with sm_30, as
was the case for gcc-5 to gcc-10.  That however reintroduces the problem from
PR97348.

Deal with PR97348 in the simplest way possible: when calling the assembler for
sm_30, specify --no-verify.

This has the unfortunate effect that after fixing PR104758 by building
libraries with sm_30, the libraries are no longer verified.  This can be
improved upon by:
- adding a configure test in gcc that tests if CUDA supports sm_30, and
  if so disabling this patch
- dealing with this in nvptx-tools somehow, either:
  - detect at ptxas execution time that it doesn't support sm_30, or
  - detect this at nvptx-tool configure time.

gcc/ChangeLog:

2022-03-03  Tom de Vries  <[email protected]>

	* config/nvptx/nvptx.h (ASM_SPEC): Add %{misa=sm_30:--no-verify}.

gcc/config/nvptx/nvptx.h

@@ -32,7 +32,7 @@
 /* Default needs to be in sync with default for misa in nvptx.opt.
    We add a default here to work around a hard-coded sm_30 default in
    nvptx-as.  */
-#define ASM_SPEC "%{misa=*:-m %*; :-m sm_35}"
+#define ASM_SPEC "%{misa=*:-m %*; :-m sm_35}%{misa=sm_30:--no-verify}"
 
 #define TARGET_CPU_CPP_BUILTINS() nvptx_cpu_cpp_builtins ()