[OpenMP][Libomptarget] Remove possible harmful copy constructor call for RTLsTy

[atmnpatel]

Summary

From https://bugs.llvm.org/show_bug.cgi?id=48973, we know that
std::call_once(PM->RTLs.initFlag, &RTLsTy::LoadRTLs, PM->RTLs) causes compile
time problems in libstdc++v3 5.3.1. This is because there was a defect in the
standard regarding the call_once (LWG 2442). This was fixed in libstdc++ soon
thereafter, but there are likely other standard libraries where this will fail.

It seems to me that the latest libstdc++ reads PM->RTLs and knows to move
PM->RTLs, while earlier implementations try to copy it, but this seems to fix
it for me at least locally, but given how finicky this could be, it'd be great
if @sylvestre.ledru could confirm it for me. The alternative is to change the
LoadRTLs signature but this should be fine.

[jdoerfert]

LG. Should hopefully fix the issue. Please also backport to the release branch.

[sylvestre.ledru]

I confirm that it fixed the problem - still occurring on 12

[atmnpatel]

Sorry I added it to the bug assuming that I couldn't actually push to the 12.x release branch, but I do have permission for that so it should be fixed there now as well.

openmp/libomptarget/src/interface.cpp

EXTERN void __tgt_register_requires(int64_t flags) {
   TIMESCOPE();
   PM->RTLs.RegisterRequires(flags);
 }
 
 ////////////////////////////////////////////////////////////////////////////////
 /// adds a target shared library to the target execution image
 EXTERN void __tgt_register_lib(__tgt_bin_desc *desc) {
   TIMESCOPE();
-  std::call_once(PM->RTLs.initFlag, &RTLsTy::LoadRTLs, PM->RTLs);
+  std::call_once(PM->RTLs.initFlag, &RTLsTy::LoadRTLs, &PM->RTLs);
   for (auto &RTL : PM->RTLs.AllRTLs) {
     if (RTL.register_lib) {
       if ((*RTL.register_lib)(desc) != OFFLOAD_SUCCESS) {
         DP("Could not register library with %s", RTL.RTLName.c_str());
       }
     }
   }
   PM->RTLs.RegisterLib(desc);