[NFC] Fix the signature and definition of findByPrefix

In https://reviews.llvm.org/rG257b29715bb27b7d9f6c3c40c481b6a4af0b37e5,
the definition of OptTable::Info::Flags was changed from `unsigned
short` to `unsigned int`, but the definition/declaration of
OptTable::findByPrefix wasn't updated to reflect that.

This patch updates findByPrefix accordingly.

llvm/include/llvm/Option/OptTable.h

@@ -152,7 +152,7 @@ class OptTable {
   ///
   /// \return The vector of flags which start with Cur.
   std::vector<std::string> findByPrefix(StringRef Cur,
-                                        unsigned short DisableFlags) const;
+                                        unsigned int DisableFlags) const;
 
   /// Find the OptTable option that most closely matches the given string.
   ///

llvm/lib/Option/OptTable.cpp

@@ -228,7 +228,7 @@ OptTable::suggestValueCompletions(StringRef Option, StringRef Arg) const {
 }
 
 std::vector<std::string>
-OptTable::findByPrefix(StringRef Cur, unsigned short DisableFlags) const {
+OptTable::findByPrefix(StringRef Cur, unsigned int DisableFlags) const {
   std::vector<std::string> Ret;
   for (size_t I = FirstSearchableIndex, E = OptionInfos.size(); I < E; I++) {
     const Info &In = OptionInfos[I];