rocshmem_config.h has a different include path when installed and built-dir (#186)

* rocshmem_config.h needs to be in a similar directory structure for
includes to work when building testers in build, and from an installed
library

* Do not change installed rocshmem.hpp

src/rocshmem_gpu.cpp

@@ -43,7 +43,7 @@
 
 #include <cstdlib>
 
-#include "rocshmem_config.h"  // NOLINT(build/include_subdir)
+#include "rocshmem/rocshmem_config.h"  // NOLINT(build/include_subdir)
 #include "rocshmem/rocshmem.hpp"
 #include "backend_bc.hpp"
 #include "context_incl.hpp"