Pre-commit test: [Preprocessor] Do not expand macros if the input is already preprocessed

Author: jmmartinez

clang/test/Preprocessor/preprocess-cpp-output.c

@@ -0,0 +1,9 @@
+// RUN: %clang_cc1 -E -x c %s | FileCheck %s --check-prefixes=EXPANDED
+// RUN: %clang_cc1 -E -x cpp-output %s | FileCheck %s --check-prefixes=EXPANDED
+
+// EXPANDED: void __attribute__((__attribute__((always_inline)))) foo()
+
+#define always_inline __attribute__((always_inline))
+void __attribute__((always_inline)) foo() {
+    return 4;
+}