[SR-2409] Rephrase diagnostic to consider Objective-C interop

When Objective-C interop is enabled, modules will continue to be referred to as “Objective-C modules”. But when interop is disabled, they will be referred to as “C modules”.

Updated the existing test for the current behavior that doesn’t expect to fail on linux and doesn’t require objc_interop, so that it checks to different diagnostics on the two systems.

Author: David Ronnqvist

include/swift/AST/DiagnosticsClangImporter.def

@@ -44,7 +44,7 @@ NOTE(note_from_clang,none,
   "%0", (StringRef))
 
 ERROR(clang_cannot_build_module,Fatal,
-  "could not build Objective-C module '%0'", (StringRef))
+  "could not build %select{C|Objective-C}0 module '%1'", (bool, StringRef))
 
 ERROR(bridging_header_missing,Fatal,
   "bridging header '%0' does not exist", (StringRef))

lib/ClangImporter/ClangDiagnosticConsumer.cpp

@@ -173,6 +173,7 @@ void ClangDiagnosticConsumer::HandleDiagnostic(
                                   clangDiag.getLocation());
 
     ctx.Diags.diagnose(loc, diag::clang_cannot_build_module,
+                       ctx.LangOpts.EnableObjCInterop,
                        CurrentImport->getName());
     return;
   }

test/ClangImporter/non-modular-include.swift

@@ -1,8 +1,9 @@
 // RUN: rm -rf %t && mkdir -p %t
-// RUN: not %target-swift-frontend -typecheck %s -I %S/Inputs/non-modular -F %S/Inputs/non-modular 2>&1 | %FileCheck %s
+// RUN: not %target-swift-frontend -typecheck %s -I %S/Inputs/non-modular -F %S/Inputs/non-modular 2>&1 | %FileCheck --check-prefix=CHECK --check-prefix=CHECK-%target-os %s
 
 // CHECK: {{.+}}/non-modular/Foo.framework/Headers/Foo.h:1:9: error: include of non-modular header inside framework module 'Foo'
-// CHECK: error: could not build Objective-C module 'Foo'
+// CHECK-macosx: error: could not build Objective-C module 'Foo'
+// CHECK-linux: error: could not build C module 'Foo'
 // CHECK-NOT: error
 
 import Foo