Add a test that we don't store stale modtime in modules

The change from r209195 turned out to be important to avoid saving stale
modification time/expected size information in a module file when there
are 3 or more modules in a dependency chain and the bottom one is
rebuilt. So add a test for that.

rdar://problem/17038180

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@209682 91177308-0d34-0410-b5e6-96231b3b80d8

test/Modules/no-stale-modtime.m

+// Ensure that when rebuilding a module we don't save its old modtime when
+// building modules that depend on it.
+
+// REQUIRES: shell
+// RUN: rm -rf %t
+// RUN: mkdir -p %t
+// This could be replaced by diamond_*, except we want to modify the top header
+// RUN: echo '@import l; @import r;' > %t/b.h
+// RUN: echo '@import t; // fromt l' > %t/l.h
+// RUN: echo '@import t; // fromt r' > %t/r.h
+// RUN: echo '// top' > %t/t.h
+// RUN: echo 'module b { header "b.h" } module l { header "l.h" }' > %t/module.map
+// RUN: echo 'module r { header "r.h" } module t { header "t.h" }' >> %t/module.map
+
+// RUN: %clang_cc1 -fmodules -fmodules-cache-path=%t -fdisable-module-hash \
+// RUN:     -I %t -fsyntax-only %s -Wmodule-build 2>&1 \
+// RUN: | FileCheck -check-prefix=REBUILD-ALL %s
+// RUN: %clang_cc1 -fmodules -fmodules-cache-path=%t -fdisable-module-hash \
+// RUN:     -I %t -fsyntax-only %s -Wmodule-build -verify
+
+// Add an identifier to ensure everything depending on t is out of date
+// RUN: echo 'extern int a;' >> %t/t.h
+// RUN: %clang_cc1 -fmodules -fmodules-cache-path=%t -fdisable-module-hash \
+// RUN:     -I %t -fsyntax-only %s -Wmodule-build 2>&1 \
+// RUN: | FileCheck -check-prefix=REBUILD-ALL %s
+// RUN: %clang_cc1 -fmodules -fmodules-cache-path=%t -fdisable-module-hash \
+// RUN:     -I %t -fsyntax-only %s -Wmodule-build -verify
+
+// REBUILD-ALL: building module 'b'
+// REBUILD-ALL: building module 'l'
+// REBUILD-ALL: building module 't'
+// REBUILD-ALL: building module 'r'
+
+// Use -verify when expecting no modules to be rebuilt.
+// expected-no-diagnostics
+
+@import b;