[Option] Remove the error-prone default argument true from 3-argument hasFlag

Author: MaskRay

llvm/include/llvm/Option/ArgList.h

@@ -298,7 +298,7 @@ class ArgList {
   /// true if the option is present, false if the negation is present, and
   /// \p Default if neither option is given. If both the option and its
   /// negation are present, the last one wins.
-  bool hasFlag(OptSpecifier Pos, OptSpecifier Neg, bool Default=true) const;
+  bool hasFlag(OptSpecifier Pos, OptSpecifier Neg, bool Default) const;
 
   /// hasFlag - Given an option \p Pos, an alias \p PosAlias and its negative
   /// form \p Neg, return true if the option or its alias is present, false if