Enhance swift-ide-test to accept -swift-version multiple times.

This allows swift-ide-test to be passed
-swift-version X by lit but have it
overriden by a specifc test.

Author: tkremenek

tools/swift-ide-test/swift-ide-test.cpp

@@ -237,7 +237,7 @@ SDK("sdk", llvm::cl::desc("path to the SDK to build against"));
 static llvm::cl::opt<std::string>
 Triple("target", llvm::cl::desc("target triple"));
 
-static llvm::cl::opt<std::string>
+static llvm::cl::list<std::string>
 SwiftVersion("swift-version", llvm::cl::desc("Swift version"));
 
 static llvm::cl::opt<std::string>
@@ -2982,8 +2982,11 @@ int main(int argc, char *argv[]) {
   if (!options::Triple.empty())
     InitInvok.setTargetTriple(options::Triple);
   if (!options::SwiftVersion.empty()) {
+    // Honor the *last* -swift-version specified.
+    const auto &LastSwiftVersion =
+      options::SwiftVersion[options::SwiftVersion.size()-1];
     if (auto swiftVersion =
-          version::Version::parseVersionString(options::SwiftVersion,
+          version::Version::parseVersionString(LastSwiftVersion,
                                                SourceLoc(), nullptr)) {
       if (auto actual = swiftVersion.getValue().getEffectiveLanguageVersion())
         InitInvok.getLangOptions().EffectiveLanguageVersion = actual.getValue();