Fix Fuchsia dyld in asan-ubsan variant

[shayba]

Summary

The Clang Fuchsia driver sets -dynamic-linker to ld.so.1 or to a variant if needed.
Fix the variant lib path in asan-ubsan variant.

See also:
https://bugs.fuchsia.dev/p/fuchsia/issues/detail?id=118344

[mcgrathr]

I don't think we want this in the generic compiler behavior. It would only make sense if the toolchain runtimes have extra versions, and I don't think we want that many extra versions.
It may be worthwhile to change the asan multilib builds to enable ubsan checks too, but I don't think we want to support two separate asan flavors in the driver.

clang/lib/Driver/ToolChains/Fuchsia.cpp

if (Args.hasArg(options::OPT_static))
     CmdArgs.push_back("-Bstatic");
   else if (Args.hasArg(options::OPT_shared))
     CmdArgs.push_back("-shared");
 
   const SanitizerArgs &SanArgs = ToolChain.getSanitizerArgs(Args);
 
   if (!Args.hasArg(options::OPT_shared) && !Args.hasArg(options::OPT_r)) {
     std::string Dyld = D.DyldPrefix;
-    if (SanArgs.needsAsanRt() && SanArgs.needsSharedRt())
+    if (SanArgs.needsAsanRt() && !SanArgs.needsUbsanRt() &&
+        SanArgs.needsSharedRt())
       Dyld += "asan/";
+    if (SanArgs.needsAsanRt() && SanArgs.needsUbsanRt() &&
+        SanArgs.needsSharedRt())
+      Dyld += "asan-ubsan/";
     if (SanArgs.needsHwasanRt() && SanArgs.needsSharedRt())
       Dyld += "hwasan/";
     if (SanArgs.needsTsanRt() && SanArgs.needsSharedRt())
       Dyld += "tsan/";
     Dyld += "ld.so.1";
     CmdArgs.push_back("-dynamic-linker");
     CmdArgs.push_back(Args.MakeArgString(Dyld));
   }