Suppress declared_but_not_referenced warning for NVHPC

  Catch2 suppresses unused variable and equivalent warnings in a couple
  of places, but most importantly, in the declaration of autoRegistrar
  here. This warning gets triggered by NVHPC compiler. The current patch
  adds three macros, namely:

      CATCH_INTERNAL_START_WARNINGS_SUPPRESSION
      CATCH_INTERNAL_SUPPRESS_UNUSED_VARIABLE_WARNINGS
      CATCH_INTERNAL_STOP_WARNINGS_SUPPRESSION

  for the NVHPC Compiler which in particular prevents that warning from
  occurring. The compiler is detected completely separately from the
  other compilers in this patch, because from what I found out, NVHPC
  defines __GNUC__ as well for some reason. (I suspect because it
  advertises itself as GNU compatible.)

src/catch2/internal/catch_compiler_capabilities.hpp

@@ -60,6 +60,12 @@
 
 #endif
 
+#if defined(__NVCOMPILER)
+#    define CATCH_INTERNAL_START_WARNINGS_SUPPRESSION _Pragma( "diag push" )
+#    define CATCH_INTERNAL_STOP_WARNINGS_SUPPRESSION  _Pragma( "diag pop" )
+#    define CATCH_INTERNAL_SUPPRESS_UNUSED_VARIABLE_WARNINGS _Pragma( "diag_suppress declared_but_not_referenced" )
+#endif
+
 #if defined(__CUDACC__) && !defined(__clang__)
 #  ifdef __NVCC_DIAG_PRAGMA_SUPPORT__
 // New pragmas introduced in CUDA 11.5+