[gardening] Fix a vs an typos.

Author: practicalswift

benchmark/utils/TestsUtils.swift

@@ -67,7 +67,7 @@ struct MyStruct : SomeProtocol {
 public func someProtocolFactory() -> SomeProtocol { return MyStruct() }
 
 // Just consume the argument.
-// It's important that this function is in a another module than the tests
+// It's important that this function is in another module than the tests
 // which are using it.
 public func blackHole<T>(_ x: T) {
 }

include/swift/AST/SourceEntityWalker.h

@@ -126,7 +126,7 @@ class SourceEntityWalker {
 
   /// This method is called for each external argument name in function-like
   /// declarations like constructor, function and subscript. The function is
-  /// called only when a external argument label is specifically specified,
+  /// called only when an external argument label is specifically specified,
   /// like func foo(External Internal: Int) {}.
   /// If it returns false, the remaining traversal is terminated and returns
   /// failure.