rocSHMEM device API changes for bitcode support (#211)

ROCSHMEM_CTX_DEFAULT's visibility needs to be explicitly set to expose that as external device global variable in device bitcode.

src/rocshmem_gpu.cpp

@@ -63,7 +63,7 @@
 
 namespace rocshmem {
 
-__device__ __constant__ rocshmem_ctx_t ROCSHMEM_CTX_DEFAULT{};
+__device__  rocshmem_ctx_t __attribute__((visibility("default"))) ROCSHMEM_CTX_DEFAULT{};
 
 __constant__ Backend *device_backend_proxy;