[clang] [SPARC][clang] Add -m(no-)v8plus flags handling (PR #98713)

[Fangrui Song via cfe-commits]

================
@@ -179,6 +179,13 @@ void sparc::getSparcTargetFeatures(const Driver &D, const ArgList &Args,
       Features.push_back("-hard-quad-float");
   }
 
+  if (Arg *A = Args.getLastArg(options::OPT_mv8plus, options::OPT_mno_v8plus)) {
+    if (A->getOption().matches(options::OPT_mv8plus))
----------------
MaskRay wrote:

We usually know whether a feature is default on or off.
If it is default off, the driver only passes `+xxx`, but suppresses `-xxx`.

Are both `+v9` and `-v9` needed here?

https://github.com/llvm/llvm-project/pull/98713