Allow passing additional compiler/linker flags for the tests

Summary:
These flags can be specified using the CMake variables
LIBCXX_TEST_LINKER_FLAGS and LIBCXX_TEST_COMPILER_FLAGS.
When building the tests for CHERI I need to pass additional
flags (such as -mabi=n64 or -mabi=purecap) to the compiler
for our test configurations

Reviewers: EricWF

Reviewed By: EricWF

Subscribers: christof, mgorny, cfe-commits

Differential Revision: https://reviews.llvm.org/D42139

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@325914 91177308-0d34-0410-b5e6-96231b3b80d8

utils/libcxx/test/config.py

@@ -510,6 +510,9 @@ class Configuration(object):
             # and so that those tests don't have to be changed to tolerate
             # this insanity.
             self.cxx.compile_flags += ['-DNOMINMAX']
+        additional_flags = self.get_lit_conf('test_compiler_flags')
+        if additional_flags:
+            self.cxx.compile_flags += shlex.split(additional_flags)
 
     def configure_default_compile_flags(self):
         # Try and get the std version from the command line. Fall back to
@@ -794,6 +797,9 @@ class Configuration(object):
                                         self.use_system_cxx_lib]
             if self.is_windows and self.link_shared:
                 self.add_path(self.cxx.compile_env, self.use_system_cxx_lib)
+        additional_flags = self.get_lit_conf('test_linker_flags')
+        if additional_flags:
+            self.cxx.link_flags += shlex.split(additional_flags)
 
     def configure_link_flags_abi_library_path(self):
         # Configure ABI library paths.