Revert "PrintAsObjC Test: Don't use modules for C compatibility header tests"

This reverts commit 0f98021.

Author: hamishknight

test/PrintAsObjC/cdecl-official.swift

@@ -12,7 +12,7 @@
 // RUN: %check-in-clang-c %t/cdecl.h -Wnullable-to-nonnull-conversion
 
 /// Build a client against cdecl.h
-// RUN: %clang-no-modules -c %t/Client.c -I %t \
+// RUN: %clang -c %t/Client.c -fmodules -I %t \
 // RUN:   -F %S/../Inputs/clang-importer-sdk-path/frameworks \
 // RUN:   -I %clang-include-dir -Werror \
 // RUN:   -isysroot %S/../Inputs/clang-importer-sdk

test/PrintAsObjC/lit.local.cfg

@@ -11,7 +11,8 @@ config.substitutions.insert(0, ('%check-in-clang',
   '-isysroot %r/Inputs/clang-importer-sdk' % config.test_source_root) )
 
 config.substitutions.insert(0, ('%check-in-clang-c',
-  '%%clang-no-modules -fsyntax-only -x c-header -std=c99 '
+  '%%clang -fsyntax-only -x c-header -std=c99 -fmodules '
+  '-fmodules-validate-system-headers '
   '-Weverything -Werror -Wno-unused-macros -Wno-incomplete-module '
   '-Wno-auto-import -Wno-poison-system-directories '
   '-F %%clang-importer-sdk-path/frameworks '

test/lit.cfg

@@ -789,11 +789,6 @@ config.substitutions.append( ('%clangxx',
                               "%r %s" %
                                 (config.clangxx, clang_mcp_opt)) )
 
-# Alternative to %clang that doesn't require -fmodules.
-config.substitutions.append( ('%clang-no-modules',
-                              "%r" %
-                                (config.clang)) )
-
 # This must come after all substitutions containing "%clang".
 # Note: %clang is the locally-built clang.
 # To get Xcode's clang, use %target-clang.