Let it compile when pmix is not found (#185)

cmake/find_pmix.cmake

@@ -57,6 +57,6 @@ macro(check_pmix)
   if (PMIX_HEADER AND PMIX_LIBRARY)
     set(PMIX_INCLUDE_DIRECTORIES ${PMIX_HEADER})
     set(PMIX_LIBRARIES ${PMIX_LIBRARY})
-    set(HAVE_PMIX TRUE)
+    set(PMIx_FOUND TRUE)
   endif()
 endmacro()