Build always and fix return value

ompi/mpiext/cuda/c/mpiext_cuda.c

@@ -23,9 +23,9 @@
 #include "opal/constants.h"
 #include "ompi/mpiext/cuda/c/mpiext_cuda_c.h"
 
-/* The fact that this code is configured and compiled means that we have CUDA aware
-   support.  We may expand on this API to return more features in the future. */
+/* If CUDA-aware support is configured in, return 1. Otherwise, return 0.
+ * This API may be extended to return more features in the future. */
 int MPIX_Query_cuda_support(void)
 {
-    return OPAL_SUCCESS;
+    return OPAL_CUDA_SUPPORT;
 }

ompi/mpiext/cuda/configure.m4

@@ -18,25 +18,10 @@ AC_DEFUN([OMPI_MPIEXT_cuda_CONFIG],[
     AC_CONFIG_FILES([ompi/mpiext/cuda/Makefile])
     AC_CONFIG_FILES([ompi/mpiext/cuda/c/Makefile])
 
-    OPAL_VAR_SCOPE_PUSH([ompi_mpi_ext_cuda_happy])
-
-    # If we don't want CUDA, don't compile this extention
+    # We compile this whether CUDA support was requested or not. It allows
+    # us to to detect if we have CUDA support.
     AS_IF([test "$ENABLE_cuda" = "1" || \
            test "$ENABLE_EXT_ALL" = "1"],
-          [ompi_mpi_ext_cuda_happy=1],
-          [ompi_mpi_ext_cuda_happy=0])
-
-    AS_IF([test "$ompi_mpi_ext_cuda_happy" = "1" && \
-           test "$CUDA_SUPPORT" = "1"],
           [$1],
-          [ # Error if the user specifically asked for this extension,
-            # but we can't build it.
-           AS_IF([test "$ENABLE_cuda" = "1"],
-                 [AC_MSG_WARN([Requested "cuda" MPI extension, but cannot build it])
-                  AC_MSG_WARN([because cuda support is not enabled.])
-                  AC_MSG_WARN([Try again with --with-cuda])
-                  AC_MSG_ERROR([Cannot continue])])
-           $2])
-
-    OPAL_VAR_SCOPE_POP
+          [$2])
 ])