[clang] Support __float128 on DragonFlyBSD.

Differential Revision: https://reviews.llvm.org/D111760

Author: fcambus

clang/lib/Basic/Targets/OSTargets.h

@@ -179,6 +179,8 @@ class LLVM_LIBRARY_VISIBILITY DragonFlyBSDTargetInfo
     Builder.defineMacro("__KPRINTF_ATTRIBUTE__");
     Builder.defineMacro("__tune_i386__");
     DefineStd(Builder, "unix", Opts);
+    if (this->HasFloat128)
+      Builder.defineMacro("__FLOAT128__");
   }
 
 public:
@@ -188,6 +190,7 @@ class LLVM_LIBRARY_VISIBILITY DragonFlyBSDTargetInfo
     default:
     case llvm::Triple::x86:
     case llvm::Triple::x86_64:
+      this->HasFloat128 = true;
       this->MCountName = ".mcount";
       break;
     }