[clang] Check '-Wp,' arg has values before accesing (#113677)

Executing `clang -Wp,` without any argument value causes Undefined
Behavior due to accessing a SmallVector without elements

Executing clang in debug mode raises an assert and Valgrind complains as
follow:

```
$ valgrind bin/clang -Wp,
==18620== Memcheck, a memory error detector
==18620== Copyright (C) 2002-2022, and GNU GPL'd, by Julian Seward et al.
==18620== Using Valgrind-3.22.0 and LibVEX; rerun with -h for copyright info
==18620== Command: bin/clang -Wp,
==18620== 
==18620== Conditional jump or move depends on uninitialised value(s)
==18620==    at 0x44F215B: clang::driver::Driver::TranslateInputArgs(llvm::opt::InputArgList const&) const (in /home/jaime/devel/llvm-project/build/bin/clang-20)
==18620==    by 0x4515831: clang::driver::Driver::BuildCompilation(llvm::ArrayRef<char const*>) (in /home/jaime/devel/llvm-project/build/bin/clang-20)
==18620==    by 0x10B3435: clang_main(int, char**, llvm::ToolContext const&) (in /home/jaime/devel/llvm-project/build/bin/clang-20)
==18620==    by 0xF78F99: main (in /home/jaime/devel/llvm-project/build/bin/clang-20)
==18620== 
...
```

Author: jgonzac

clang/lib/Driver/Driver.cpp

@@ -454,6 +454,7 @@ DerivedArgList *Driver::TranslateInputArgs(const InputArgList &Args) const {
     // some build systems. We don't try to be complete here because we don't
     // care to encourage this usage model.
     if (A->getOption().matches(options::OPT_Wp_COMMA) &&
+        A->getNumValues() > 0 &&
         (A->getValue(0) == StringRef("-MD") ||
          A->getValue(0) == StringRef("-MMD"))) {
       // Rewrite to -MD/-MMD along with -MF.