libc++ testing: allow to provide a path for `use_system_cxx_lib`

[mehdi_amini]

Summary

As we're trying to setup testing / bots for all shipping version of libc++
on macOS/iOS, we'll need to be able to pass a path to where to find the
dylib for each previous version of the OS.

[EricWF]

LGTM.

libcxx/trunk/utils/libcxx/test/config.py

def configure_cxx_library_root(self):
         self.cxx_runtime_root = self.get_lit_conf('cxx_runtime_root',
                                                    self.cxx_library_root)
 
     def configure_use_system_cxx_lib(self):
         # This test suite supports testing against either the system library or
         # the locally built one; the former mode is useful for testing ABI
         # compatibility between the current headers and a shipping dynamic
         # library.
-        self.use_system_cxx_lib = self.get_lit_bool('use_system_cxx_lib')
-        if self.use_system_cxx_lib is None:
-            # Default to testing against the locally built libc++ library.
+        self.use_system_cxx_lib = self.get_lit_conf('use_system_cxx_lib')
+        if self.use_system_cxx_lib == 'true':
+            self.use_system_cxx_lib = True
+        elif self.use_system_cxx_lib == 'false':
             self.use_system_cxx_lib = False
-            self.lit_config.note(
-                "inferred use_system_cxx_lib as: %r" % self.use_system_cxx_lib)
+        else:
+            assert os.path.isdir(self.use_system_cxx_lib)
 
     def configure_cxx_stdlib_under_test(self):
         self.cxx_stdlib_under_test = self.get_lit_conf(
             'cxx_stdlib_under_test', 'libc++')
         if self.cxx_stdlib_under_test not in \
                 ['libc++', 'libstdc++', 'msvc', 'cxx_default']:
             self.lit_config.fatal(
                 'unsupported value for "cxx_stdlib_under_test": %s'
def configure_link_flags_cxx_library_path(self):
                 if self.is_windows and self.link_shared:
                     self.add_path(self.cxx.compile_env, self.cxx_library_root)
             if self.cxx_runtime_root:
                 if not self.is_windows:
                     self.cxx.link_flags += ['-Wl,-rpath,' +
                                             self.cxx_runtime_root]
                 elif self.is_windows and self.link_shared:
                     self.add_path(self.exec_env, self.cxx_runtime_root)
+        elif os.path.isdir(str(self.use_system_cxx_lib)):
+            self.cxx.link_flags += ['-L' + self.use_system_cxx_lib]
+            if not self.is_windows:
+                self.cxx.link_flags += ['-Wl,-rpath,' +
+                                        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)
 
     def configure_link_flags_abi_library_path(self):
         # Configure ABI library paths.
         self.abi_library_root = self.get_lit_conf('abi_library_path')
         if self.abi_library_root:
             self.cxx.link_flags += ['-L' + self.abi_library_root]
             if not self.is_windows:
                 self.cxx.link_flags += ['-Wl,-rpath,' + self.abi_library_root]

libcxx/trunk/utils/libcxx/test/target_info.py

class DarwinLocalTI(DefaultTargetInfo):
 
     def add_cxx_link_flags(self, flags):
         flags += ['-lSystem']
 
     def configure_env(self, env):
         library_paths = []
         # Configure the library path for libc++
         if self.full_config.use_system_cxx_lib:
+            if (os.path.isdir(str(self.full_config.use_system_cxx_lib))):
+                library_paths += [self.full_config.use_system_cxx_lib]
             pass
         elif self.full_config.cxx_runtime_root:
             library_paths += [self.full_config.cxx_runtime_root]
         # Configure the abi library path
         if self.full_config.abi_library_root:
             library_paths += [self.full_config.abi_library_root]
         if library_paths:
             env['DYLD_LIBRARY_PATH'] = ':'.join(library_paths)