Expose ProvidePositionalOption as a public API

The motivation is to reuse the key value parsing logic here to
parse instance specific pass options within the context of MLIR.
The primary functionality exposed is the "," splitting for
arrays and the logic for properly handling duplicate definitions
of a single flag.

Patch by: Parker Schuh <parkers@google.com>

Differential Revision: https://reviews.llvm.org/D68294

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@373815 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Support/CommandLine.h

@@ -2000,6 +2000,9 @@ void ResetAllOptionOccurrences();
 /// where no options are supported.
 void ResetCommandLineParser();
 
+/// Parses `Arg` into the option handler `Handler`.
+bool ProvidePositionalOption(Option *Handler, StringRef Arg, int i);
+
 } // end namespace cl
 
 } // end namespace llvm

lib/Support/CommandLine.cpp

@@ -692,7 +692,7 @@ static inline bool ProvideOption(Option *Handler, StringRef ArgName,
   return false;
 }
 
-static bool ProvidePositionalOption(Option *Handler, StringRef Arg, int i) {
+bool llvm::cl::ProvidePositionalOption(Option *Handler, StringRef Arg, int i) {
   int Dummy = i;
   return ProvideOption(Handler, Handler->ArgStr, Arg, 0, nullptr, Dummy);
 }