Functional tests without MPI support (#343)

* Let functional tests build without external MPI

* Fix error conditions when using uuid startup with internal MPI

* Do not abort if libibverbs is not found but not using GDA

* Enabled RO functional test initialized with TEST_UUID

* Reduce load time for ro backend_can_run and prevent mpilib_dlclose
crashing

* Fix case TEST_UUID=1, ROCSHMEM_BACKEND='' (autoloading gda)

src/reverse_offload/backend_ro.cpp

@@ -33,6 +33,7 @@
 #include <cstdlib>
 #include <memory>
 #include <thread>  // NOLINT
+#include <dlfcn.h>
 
 #include "rocshmem/rocshmem.hpp"
 #include "atomic_return.hpp"
@@ -131,6 +132,19 @@ ROBackend::ROBackend(MPI_Comm comm)
   *done_init = 1;
 }
 
+/* Currently we only check whether we can dlopen an MPI library.
+ */
+int ROBackend::backend_can_run() {
+  auto handle = dlopen("libmpi.so", RTLD_LAZY);
+  if (!handle) {
+    printf("Could not open libmpi.so. Returning\n");
+    return ROCSHMEM_ERROR;
+  }
+  //TODO dlsym MPI_Get_library_version and verify compat when HAVE_EXTERNAL_MPI is undef
+  dlclose(handle);
+  return ROCSHMEM_SUCCESS;
+}
+
 void ROBackend::setup_ctxs() {
   CHECK_HIP(hipMalloc(&ctx_array, sizeof(ROContext) * envvar::max_num_contexts));
   for (size_t i = 0; i < envvar::max_num_contexts; i++) {