test: use inferSwiftBinary to find the reflection tool

We would previously search for it in the path rather than the build
tree.  This should identify where the tool is being used from, provide
the just built tool, and still allow the user to change the tool path by
an environment variable.

Author: compnerd

test/lit.cfg

@@ -1594,8 +1594,7 @@ config.substitutions.append(('%target-swift-ide-test\(mock-sdk:([^)]+)\)',
 config.substitutions.append(('%target-swift-ide-test', "%s -swift-version %s" % (config.target_swift_ide_test, swift_version)))
 
 if not hasattr(config, 'target_swift_reflection_test'):
-    config.target_swift_reflection_test = lit.util.which(
-        swift_reflection_test_name, config.environment['PATH'])
+    config.target_swift_reflection_test = inferSwiftBinary(swift_reflection_test_name)
 
 config.substitutions.append(('%target-swift-reflection-test', config.target_swift_reflection_test))