[libc++] Enable additional tests when Clang modules are enabled

Disabling tests when Clang modules are enabled is not great because
we are moving more and more tests towards using Clang modules by
default. Instead, disable Clang modules on a per-test basis.

Author: ldionne

libcxx/test/extensions/libcxx/depr/depr.c.headers/extern_c.pass.cpp

@@ -8,7 +8,7 @@
 
 // When building with modules, including headers inside extern "C" is an anti-pattern
 // that we don't want to support and can't support with LSV enabled.
-// UNSUPPORTED: clang-modules-build
+// ADDITIONAL_COMPILE_FLAGS: -fno-modules
 
 // Sometimes C++'s <foo.h> headers get included within extern "C" contexts. This
 // is ill-formed (no diagnostic required), per [using.headers]p3, but we permit

libcxx/test/extensions/libcxx/depr/depr.c.headers/include_as_c.sh.cpp

@@ -7,7 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 // We're building as C, so this test doesn't work when building with modules.
-// UNSUPPORTED: clang-modules-build
+// ADDITIONAL_COMPILE_FLAGS: -fno-modules
 
 // GCC complains about unrecognized arguments because we're compiling the
 // file as C, but we're passing C++ flags on the command-line.

libcxx/test/extensions/libcxx/depr/depr.c.headers/stdint_h.xopen_source.compile.pass.cpp

@@ -7,7 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 // This test breaks when enabling LSV.
-// UNSUPPORTED: clang-modules-build
+// ADDITIONAL_COMPILE_FLAGS: -fno-modules
 
 // Test that limits macros are available when <stdint.h> is included
 // with or without macro _XOPEN_SOURCE=700.

libcxx/test/extensions/posix/xopen_source.gen.py

@@ -15,7 +15,7 @@
 # Some parts of the code like <fstream> use non-standard functions in their implementation,
 # and these functions are not provided when _XOPEN_SOURCE is set to older values. This
 # breaks when building with modules even when we don't use the offending headers directly.
-# UNSUPPORTED: clang-modules-build
+# ADDITIONAL_COMPILE_FLAGS: -fno-modules
 
 # The AIX localization support uses some functions as part of their headers that require a
 # recent value of _XOPEN_SOURCE.

libcxx/test/libcxx-03/assertions/customize_verbose_abort.compile-time.pass.cpp

@@ -7,7 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 // This compile-time customization requires cross-file macros, which doesn't work with modules.
-// UNSUPPORTED: clang-modules-build
+// ADDITIONAL_COMPILE_FLAGS: -fno-modules
 
 // Make sure that we can customize the verbose termination function at compile-time by
 // defining _LIBCPP_VERBOSE_ABORT ourselves. Note that this does not have any

libcxx/test/libcxx-03/assertions/modes/hardening_mode_incorrect_value.sh.cpp

@@ -9,10 +9,11 @@
 // This test verifies that setting the hardening mode to a value that's not part of the predefined constants triggers
 // a compile-time error.
 
-// Modules build produces a different error ("Could not build module 'std'").
-// UNSUPPORTED: clang-modules-build
 // REQUIRES: verify-support
 
+// TODO: Investigate
+// ADDITIONAL_COMPILE_FLAGS: -fno-modules
+
 // Note that GCC doesn't support `-Wno-macro-redefined`.
 // RUN: %{verify} -U_LIBCPP_HARDENING_MODE -D_LIBCPP_HARDENING_MODE=42
 // Make sure that common cases of misuse produce readable errors. We deliberately disallow setting the hardening mode as

libcxx/test/libcxx-03/transitive_includes.gen.py

@@ -77,7 +77,7 @@
 
 // When built with modules, this test doesn't work because --trace-includes doesn't
 // report the stack of includes correctly.
-// UNSUPPORTED: clang-modules-build
+// ADDITIONAL_COMPILE_FLAGS: -fno-modules
 
 // This test uses --trace-includes, which is not supported by GCC.
 // UNSUPPORTED: gcc

libcxx/test/libcxx-03/utilities/utility/pairs/pairs.pair/abi.non_trivial_copy_move.pass.cpp

@@ -8,7 +8,7 @@
 
 // The test suite needs to define the ABI macros on the command line when
 // modules are enabled.
-// UNSUPPORTED: clang-modules-build
+// ADDITIONAL_COMPILE_FLAGS: -fno-modules
 
 // <utility>
 

libcxx/test/libcxx/algorithms/alg.modifying.operations/copy_move_nontrivial.pass.cpp

@@ -7,11 +7,13 @@
 //===----------------------------------------------------------------------===//
 
 // UNSUPPORTED: c++03, c++11, c++14, c++17
-// In the modules build, adding another overload of `memmove` doesn't work.
-// UNSUPPORTED: clang-modules-build
+
 // GCC complains about "ambiguating" `__builtin_memmove`.
 // UNSUPPORTED: gcc
 
+// In the modules build, adding another overload of `memmove` doesn't work.
+// ADDITIONAL_COMPILE_FLAGS: -fno-modules
+
 // <algorithm>
 
 #include <cassert>

libcxx/test/libcxx/algorithms/alg.modifying.operations/copy_move_trivial.pass.cpp

@@ -7,11 +7,13 @@
 //===----------------------------------------------------------------------===//
 
 // UNSUPPORTED: c++03, c++11, c++14, c++17
-// In the modules build, adding another overload of `memmove` doesn't work.
-// UNSUPPORTED: clang-modules-build
+
 // GCC complains about "ambiguating" `__builtin_memmove`.
 // UNSUPPORTED: gcc
 
+// In the modules build, adding another overload of `memmove` doesn't work.
+// ADDITIONAL_COMPILE_FLAGS: -fno-modules
+
 // <algorithm>
 
 // These tests check that `std::copy` and `std::move` (including their variations like `copy_n`) forward to