[libcxx] [test] Add a MinGW target

This can't easily be autodetected (unless LIBCXX_TARGET_TRIPLE is
specified, or unless we query what the compiler's default target is,
which only is supported by clang), but can be chosen manually via
LIBCXX_TARGET_INFO.

This chooses mingw style lib naming, and uses -nostdlibc++ instead
of -nodefaultlib -nostdlib (as the latter requires specifying a lot of
details manually - this is done in the cmake config though).

Differential Revision: https://reviews.llvm.org/D97294

libcxx/utils/libcxx/test/config.py

@@ -109,7 +109,7 @@ class Configuration(object):
 
     def make_static_lib_name(self, name):
         """Return the full filename for the specified library name"""
-        if self.target_info.is_windows():
+        if self.target_info.is_windows() and not self.target_info.is_mingw():
             assert name == 'c++'  # Only allow libc++ to use this function for now.
             return 'lib' + name + '.lib'
         else:
@@ -382,9 +382,12 @@ class Configuration(object):
 
         # Configure libraries
         if self.cxx_stdlib_under_test == 'libc++':
-            self.cxx.link_flags += ['-nodefaultlibs']
+            if self.target_info.is_mingw():
+                self.cxx.link_flags += ['-nostdlib++']
+            else:
+                self.cxx.link_flags += ['-nodefaultlibs']
             # FIXME: Handle MSVCRT as part of the ABI library handling.
-            if self.target_info.is_windows():
+            if self.target_info.is_windows() and not self.target_info.is_mingw():
                 self.cxx.link_flags += ['-nostdlib']
             self.configure_link_flags_cxx_library()
             self.configure_link_flags_abi_library()

libcxx/utils/libcxx/test/target_info.py

@@ -27,6 +27,9 @@ class DefaultTargetInfo(object):
     def is_windows(self):
         return self.platform() == 'win32'
 
+    def is_mingw(self):
+        return False
+
     def is_darwin(self):
         return self.platform() == 'darwin'
 
@@ -184,6 +187,13 @@ class WindowsLocalTI(DefaultTargetInfo):
     def __init__(self, full_config):
         super(WindowsLocalTI, self).__init__(full_config)
 
+class MingwLocalTI(WindowsLocalTI):
+    def __init__(self, full_config):
+        super(MingwLocalTI, self).__init__(full_config)
+
+    def is_mingw(self):
+        return True
+
 def make_target_info(full_config):
     default = "libcxx.test.target_info.LocalTI"
     info_str = full_config.get_lit_conf('target_info', default)