[llvm] Drop explicit conversions of string literals to StringRef (NFC)

We routinely rely on implicit conversions of string literals to
StringRef so that we can use operator==(StringRef, StringRef).

Author: kazutakahirata

llvm/lib/Frontend/OpenMP/OMPContext.cpp

@@ -63,7 +63,7 @@ OMPContext::OMPContext(bool IsDeviceCompilation, Triple TargetTriple) {
   if (TraitSelector::TraitSelectorEnum == TraitSelector::device_arch) {        \
     if (TargetTriple.getArch() == TargetTriple.getArchTypeForLLVMName(Str))    \
       ActiveTraits.set(unsigned(TraitProperty::Enum));                         \
-    if (StringRef(Str) == StringRef("x86_64") &&                               \
+    if (StringRef(Str) == "x86_64" &&                                          \
         TargetTriple.getArch() == Triple::x86_64)                              \
       ActiveTraits.set(unsigned(TraitProperty::Enum));                         \
   }

llvm/lib/Object/MachOObjectFile.cpp

@@ -3256,13 +3256,13 @@ MachOAbstractFixupEntry::MachOAbstractFixupEntry(Error *E,
   for (const auto &Command : O->load_commands()) {
     if (Command.C.cmd == MachO::LC_SEGMENT) {
       MachO::segment_command SLC = O->getSegmentLoadCommand(Command);
-      if (StringRef(SLC.segname) == StringRef("__TEXT")) {
+      if (StringRef(SLC.segname) == "__TEXT") {
         TextAddress = SLC.vmaddr;
         break;
       }
     } else if (Command.C.cmd == MachO::LC_SEGMENT_64) {
       MachO::segment_command_64 SLC_64 = O->getSegment64LoadCommand(Command);
-      if (StringRef(SLC_64.segname) == StringRef("__TEXT")) {
+      if (StringRef(SLC_64.segname) == "__TEXT") {
         TextAddress = SLC_64.vmaddr;
         break;
       }

llvm/lib/Target/Mips/MipsISelLowering.cpp

@@ -3234,8 +3234,7 @@ MipsTargetLowering::LowerCall(TargetLowering::CallLoweringInfo &CLI,
 
   // Note: The check on the calling convention below must match
   //       MipsABIInfo::GetCalleeAllocdArgSizeInBytes().
-  bool MemcpyInByVal = ES &&
-                       StringRef(ES->getSymbol()) == StringRef("memcpy") &&
+  bool MemcpyInByVal = ES && StringRef(ES->getSymbol()) == "memcpy" &&
                        CallConv != CallingConv::Fast &&
                        Chain.getOpcode() == ISD::CALLSEQ_START;