implement -msave-args in clang/llvm, like the sun did for gcc 

Index: clang/lib/Basic/Targets/X86.cpp
--- clang/lib/Basic/Targets/X86.cpp.orig
+++ clang/lib/Basic/Targets/X86.cpp
@@ -309,6 +309,8 @@ bool X86TargetInfo::handleTargetFeatures(std::vector<s
       HasPTWRITE = true;
     } else if (Feature == "+invpcid") {
       HasINVPCID = true;
+    } else if (Feature == "+save-args") {
+      HasSaveArgs = true;
     } else if (Feature == "+enqcmd") {
       HasENQCMD = true;
     } else if (Feature == "+hreset") {
@@ -984,6 +986,7 @@ bool X86TargetInfo::hasFeature(StringRef Feature) cons
       .Case("movbe", HasMOVBE)
       .Case("movdiri", HasMOVDIRI)
       .Case("movdir64b", HasMOVDIR64B)
+      .Case("save-args", HasSaveArgs)
       .Case("mwaitx", HasMWAITX)
       .Case("pclmul", HasPCLMUL)
       .Case("pconfig", HasPCONFIG)
