OpenMP/nvptx: support 'arch(nvptx64)' as context selector

The main 'arch' context selector for nvptx is, well, 'nvptx';
however, as 'nvptx64' is used as by LLVM, it makes sense
to support it as well.

Note that LLVM has: "The triple architecture can be one of
``nvptx`` (32-bit PTX) or ``nvptx64`` (64-bit PTX)."
GCC effectively only supports the 64bit variant (at least for
offloading). Thus, GCC's 'nvptx' is not quite the same as LLVM's.

The device-compiler part (nvptx_omp_device_kind_arch_isa) uses
TARGET_ABI64 such that nvptx64 is only defined with -m64.

gcc/ChangeLog:

	* config/nvptx/gen-omp-device-properties.sh: Add 'nvptx64' to arch.
	* config/nvptx/nvptx.cc (nvptx_omp_device_kind_arch_isa): Likewise.

libgomp/ChangeLog:

	* libgomp.texi (OpenMP Context Selectors): Add 'nvptx64' as additional
	'arch' value for nvptx.

gcc/config/nvptx/gen-omp-device-properties.sh

@@ -23,7 +23,7 @@ nvptx_sm_def="$1/nvptx-sm.def"
 sms=$(grep ^NVPTX_SM $nvptx_sm_def | sed 's/.*(//;s/,.*//')
 
 echo kind: gpu
-echo arch: nvptx
+echo arch: nvptx nvptx64
 
 isa=""
 for sm in $sms; do

gcc/config/nvptx/nvptx.cc

@@ -6403,7 +6403,8 @@ nvptx_omp_device_kind_arch_isa (enum omp_device_kind_arch_isa trait,
     case omp_device_kind:
       return strcmp (name, "gpu") == 0;
     case omp_device_arch:
-      return strcmp (name, "nvptx") == 0;
+      return (strcmp (name, "nvptx") == 0
+	      || (TARGET_ABI64 && strcmp (name, "nvptx64") == 0));
     case omp_device_isa:
 #define NVPTX_SM(XX, SEP)				\
       {							\

libgomp/libgomp.texi

@@ -6098,7 +6098,7 @@ on more architectures, GCC currently does not match any @code{arch} or
 @item @code{amdgcn}, @code{gcn}
       @tab See @code{-march=} in ``AMD GCN Options''@footnote{Additionally,
       @code{gfx803} is supported as an alias for @code{fiji}.}
-@item @code{nvptx}
+@item @code{nvptx}, @code{nvptx64}
       @tab See @code{-march=} in ``Nvidia PTX Options''
 @end multitable