[libcxx] [test] Fix detection of clang-cl when cross compiling

[mstorsjo]

Summary

When cross compiling, the compiler tool doesn't have a .exe suffix.

[curdeius]

When cross-compiling (I imagine that you build on Linux and test on Windows), it seems logical to be using WindowsRemoteTI, no?
I understand that it's not there and would be almost identical to WindowsLocalTI, but it would make things clearer IMO.

Another thing, wouldn't LinuxRemoteTI will have is_windows set to True when cross-compiling from Windows, and so need the analogical treatment as you do for Windows here?

[mstorsjo]

In D98026#2606651, @curdeius wrote:

When cross-compiling (I imagine that you build on Linux and test on Windows), it seems logical to be using WindowsRemoteTI, no?
I understand that it's not there and would be almost identical to WindowsLocalTI, but it would make things clearer IMO.

Yeah maybe, but so far I don't see the benefit in adding essentially a separate duplicate copy of each of these classes, when I so far haven't seen any case where it would warrant a difference between the local and remote versions. (We have one remote version so far, LinuxRemoteTI, and that one is functionally equivalent to LinuxLocalTI.) But I agree that it's an inconsistency that we have one such but not more than that.

Another thing, wouldn't LinuxRemoteTI will have is_windows set to True when cross-compiling from Windows, and so need the analogical treatment as you do for Windows here?

Yes that's true, so maybe we should move all of the implementations of is_windows, is_darwin etc into the platform specific subclasses, and have the base class versions only return false.

Maybe it'd be best if I split this patch into two; one for just fixing clang-cl matching, and one for moving the is_* functions into subclasses?

[mstorsjo]

Split out the target info change, keeping only the clang-cl detection

[curdeius]

This part definitely LGTM.

For the target infos, I don't know what the best course of action should be, but certainly there's a place for improvement.

libcxx/utils/libcxx/test/config.py

def get_test_format(self):
             self.use_clang_verify,
             self.executor,
             exec_env=self.exec_env)
 
     def configure_cxx(self):
         # Gather various compiler parameters.
         cxx = self.get_lit_conf('cxx_under_test')
         self.cxx_is_clang_cl = cxx is not None and \
-                               os.path.basename(cxx) == 'clang-cl.exe'
+                               os.path.basename(cxx).startswith('clang-cl')
         # If no specific cxx_under_test was given, attempt to infer it as
         # clang++.
         if cxx is None or self.cxx_is_clang_cl:
             search_paths = self.config.environment['PATH']
             if cxx is not None and os.path.isabs(cxx):
                 search_paths = os.path.dirname(cxx)
             clangxx = libcxx.util.which('clang++', search_paths)
             if clangxx: