Fix spelling error (mathing >> matching)

CMakeLists.txt

@@ -289,7 +289,7 @@ if(NOT EXISTS "${CLANG_MAIN_INCLUDE_DIR}/clang/AST/Decl.h")
 endif()
 
 # This could be computed using ${CMAKE_CFG_INTDIR} if we want to link Swift
-# against a mathing LLVM build configuration.  However, we usually want to be
+# against a matching LLVM build configuration.  However, we usually want to be
 # flexible and allow linking a debug Swift against optimized LLVM.
 set(LLVM_RUNTIME_OUTPUT_INTDIR "${LLVM_BINARY_DIR}")
 set(LLVM_LIBRARY_OUTPUT_INTDIR "${LLVM_LIBRARY_DIR}")