[Modules][NFC] Rewrite friend-definition-2.cpp with split-file (#112380)

Instead of the pragmas, which are less familiar to people.
This is a follow-up of a discussion from #111992.

Author: ilya-biryukov

clang/test/Modules/friend-definition-2.cpp

@@ -1,32 +1,53 @@
-// RUN: %clang_cc1 -std=c++14 -fmodules %s -verify
-// RUN: %clang_cc1 -std=c++14 -fmodules %s -verify -triple i686-windows
-// expected-no-diagnostics
-#pragma clang module build A
-module A {}
-#pragma clang module contents
-#pragma clang module begin A
+// RUN: split-file %s %t
+
+// RUN: %clang_cc1 -std=c++14 -x c++ -fmodules -fmodule-name=A -emit-module %t/a.modulemap -o %t/a.pcm
+// RUN: %clang_cc1 -std=c++14 -x c++ -fmodules -fmodule-name=B -emit-module %t/b.modulemap -o %t/b.pcm
+// RUN: %clang_cc1 -std=c++14 -x c++ -fmodules -fmodule-map-file=%t/a.modulemap -fmodule-map-file=%t/b.modulemap \
+// RUN:   -fmodule-file=%t/a.pcm -fmodule-file=%t/b.pcm \
+// RUN:   %t/use.cc -verify
+
+// RUN: rm -f %t/*.pcm
+
+// RUN: %clang_cc1 -std=c++14 -x c++ -fmodules -fmodule-name=A -emit-module %t/a.modulemap -o %t/a.pcm -triple i686-windows
+// RUN: %clang_cc1 -std=c++14 -x c++ -fmodules -fmodule-name=B -emit-module %t/b.modulemap -o %t/b.pcm -triple i686-windows
+// RUN: %clang_cc1 -std=c++14 -x c++ -fmodules -fmodule-map-file=%t/a.modulemap -fmodule-map-file=%t/b.modulemap \
+// RUN:   -fmodule-file=%t/a.pcm -fmodule-file=%t/b.pcm \
+// RUN:   %t/use.cc -verify -triple i686-windows
+
+//--- a.modulemap
+module A {
+  header "a.h"
+}
+
+//--- a.h
+#ifndef A_H
+#define A_H
+template<typename T> struct ct { friend auto operator-(ct, ct) { struct X {}; return X(); } void x(); };
+#endif
+
+//--- b.modulemap
+module B {
+  header "b.h"
+}
+
+//--- b.h
+#ifndef B_H
+#define B_H
 template<typename T> struct ct { friend auto operator-(ct, ct) { struct X {}; return X(); } void x(); };
-#pragma clang module end
-#pragma clang module endbuild
-
-#pragma clang module build B
-module B {}
-#pragma clang module contents
-#pragma clang module begin B
-template<typename T> struct ct { friend auto operator-(ct, ct) { struct X{}; return X(); } void x(); };
 inline auto f() { return ct<float>() - ct<float>(); }
-#pragma clang module end
-#pragma clang module endbuild
+#endif
 
+//--- use.cc
+// expected-no-diagnostics
 // Force the definition of ct in module A to be the primary definition.
-#pragma clang module import A
+#include "a.h"
 template<typename T> void ct<T>::x() {}
 
 // Attempt to cause the definition of operator- in the ct primary template in
 // module B to be the primary definition of that function. If that happens,
 // we'll be left with a class template ct that appears to not contain a
 // definition of the inline friend function.
-#pragma clang module import B
+#include "b.h"
 auto v = f();
 
 ct<int> make();