[clang] Fix a misleading variable name. NFC.

[ikudrin]

Summary

The variable is true when frame pointers should be omitted in leaf functions, not kept.

[MaskRay]

Looks great! (I did notice this but I forgot to update it)

clang/lib/Driver/ToolChains/Clang.cpp

getFramePointerKind(const ArgList &Args, const llvm::Triple &Triple) {
   //
   //  "omit" options taking precedence over "no-omit" options is the only way
   //  to make 3 valid states representable
   Arg *A = Args.getLastArg(options::OPT_fomit_frame_pointer,
                            options::OPT_fno_omit_frame_pointer);
   bool OmitFP = A && A->getOption().matches(options::OPT_fomit_frame_pointer);
   bool NoOmitFP =
       A && A->getOption().matches(options::OPT_fno_omit_frame_pointer);
-  bool KeepLeaf = Args.hasFlag(options::OPT_momit_leaf_frame_pointer,
+  bool OmitLeafFP = Args.hasFlag(options::OPT_momit_leaf_frame_pointer,
                                  options::OPT_mno_omit_leaf_frame_pointer,
                                  Triple.isAArch64() || Triple.isPS4CPU());
   if (NoOmitFP || mustUseNonLeafFramePointerForTarget(Triple) ||
       (!OmitFP && useFramePointerForTargetByDefault(Args, Triple))) {
-    if (KeepLeaf)
+    if (OmitLeafFP)
       return CodeGenOptions::FramePointerKind::NonLeaf;
     return CodeGenOptions::FramePointerKind::All;
   }
   return CodeGenOptions::FramePointerKind::None;
 }
 
 /// Add a CC1 option to specify the debug compilation directory.
 static void addDebugCompDirArg(const ArgList &Args, ArgStringList &CmdArgs,