Apply constexpr on global constant varaibles

When HIP_ENABLE_DEFERRED_LOADING=0, many global variables will be
referenced but they are not initialized in that early time. The patch
will use constexpr to initialze global constant varables in compile
time.

Change-Id: I9d538b7abc6a0ce700ec3332b97fc144db5fc1ef

rocclr/device/comgrctx.cpp

@@ -31,7 +31,7 @@ bool Comgr::is_ready_ = false;
 bool Comgr::LoadLib() {
 #if defined(COMGR_DYN_DLL)
   ClPrint(amd::LOG_INFO, amd::LOG_CODE, "Loading COMGR library.");
-  static const char* ComgrLibName =
+  static constexpr const char* ComgrLibName =
     LP64_SWITCH(WINDOWS_SWITCH("amd_comgr32.dll", "libamd_comgr32.so.1"),
                 WINDOWS_SWITCH("amd_comgr.dll", "libamd_comgr.so.1"));
   cep_.handle = Os::loadLibrary(ComgrLibName);