[Clang][Driver][Hurd] Enable __float128 support on x86 on Hurd

It works fine, and this makes the Hurd driver more consistent with other
drivers.

Author: pinotree

clang/lib/Basic/Targets/OSTargets.h

@@ -328,9 +328,21 @@ class LLVM_LIBRARY_VISIBILITY HurdTargetInfo : public OSTargetInfo<Target> {
       Builder.defineMacro("_REENTRANT");
     if (Opts.CPlusPlus)
       Builder.defineMacro("_GNU_SOURCE");
+    if (this->HasFloat128)
+      Builder.defineMacro("__FLOAT128__");
   }
 public:
-  using OSTargetInfo<Target>::OSTargetInfo;
+  HurdTargetInfo(const llvm::Triple &Triple, const TargetOptions &Opts)
+      : OSTargetInfo<Target>(Triple, Opts) {
+    switch (Triple.getArch()) {
+    default:
+      break;
+    case llvm::Triple::x86:
+    case llvm::Triple::x86_64:
+      this->HasFloat128 = true;
+      break;
+    }
+  }
 };
 
 // Linux target