[OpenMP] Add -Bsymbolic to arguments for GNU linker

[jhuber6]

Summary

This patch adds the '-Bsymbolic' flag when we perform linking for the
offloading device. We already pass '-fvisibility=protected' but this is
not properly handled when using the bfd linker as is described in
https://maskray.me/blog/2021-05-16-elf-interposition-and-bsymbolic.
Previously this caused linker errors when creating the shared library.

[jhuber6]

Clang format.

[JonChesterfield]

Can we drop an xfail in an existing test as part of this patch?

clang/lib/Driver/ToolChains/Gnu.cpp

576

Perhaps a comment to the effect that the symbols are protected which makes Bsymbolic redundant, except in that it works around an issue in bfd?

[jhuber6]

In D119018#3297391, @JonChesterfield wrote:

Can we drop an xfail in an existing test as part of this patch?

We can drop an XFAIL for AMDGPU, but that's not related to the problem this fixes, we don't have any XFAIL lines for x86 tests.

[jhuber6]

More informative comment.

[JonChesterfield]

Thanks!

clang/lib/Driver/ToolChains/Gnu.cpp

if (ToolChain.ShouldLinkCXXStdlib(Args)) {
       if (OnlyLibstdcxxStatic)
         CmdArgs.push_back("-Bstatic");
       ToolChain.AddCXXStdlibLibArgs(Args, CmdArgs);
       if (OnlyLibstdcxxStatic)
         CmdArgs.push_back("-Bdynamic");
     }
     CmdArgs.push_back("-lm");
   }
+
+  // If we are linking for the device all symbols should be bound locally. The
+  // symbols are already protected which makes this redundant. This is only
+  // necessary to work around a problem in bfd.
+  // TODO: Remove this once 'lld' becomes the only linker for offloading.
+  if (JA.isDeviceOffloading(Action::OFK_OpenMP))
+    CmdArgs.push_back("-Bsymbolic");
+
   // Silence warnings when linking C code with a C++ '-stdlib' argument.
   Args.ClaimAllArgs(options::OPT_stdlib_EQ);
 
   if (!Args.hasArg(options::OPT_nostdlib, options::OPT_r)) {
     if (!Args.hasArg(options::OPT_nodefaultlibs)) {
       if (IsStatic || IsStaticPIE)
         CmdArgs.push_back("--start-group");