[build.py] Add `VCINSTALLDIR` to default variables

[aleksandr.urakov]

Summary

On my system, clang-cl can't compile tests containing char16_t and char32_t types without this environment variable defined. This fix makes the tests to pass, but I'm not sure about the such solution. What do you think about it?

[labath]

I don't think this should be necessary. Based on my experiments, the fact whether clang-cl defines char32_t depends on the version of visual studio it is emulating (-fms-compatibility-version). For instance I can do this:

$ cat /tmp/a.cc 
char32_t XX;
$ bin/clang-cl /tmp/a.cc /GS- /GR- /c -fms-compatibility-version=18
/tmp/a.cc(1,1) :  error: unknown type name 'char32_t'
char32_t XX;
^
1 error generated.
$ bin/clang-cl /tmp/a.cc /GS- /GR- /c -fms-compatibility-version=19
$ bin/clang-cl /tmp/a.cc /GS- /GR- /c

So, what I suspect is happening is that clang uses %VCINSTALLDIR% to detect the MSVC version, and then sets the compatibility based on that. If the detected version is high enough, char32_t will be automatically defined. The interesting part is that, for me, the default version seems to be high enough that even without any special setting char32_t "just works". However, I'm on linux, so the differences could be due to that.

So I think this is good news. I hope all that's needed here is to get build.py to add the -fms-compatibility thingy and things should work. Until we actually need to vary this version, I think we can just unconditionally add that flag to all clang-cl invocations in build.py.

[aleksandr.urakov]

I've checked your solution, and it's worked for me too! I think that your solution is better because it is more straight-forward. Here is the updated patch.

[labath]

This looks good to me, but let's wait for zachary too.

In D57809#1386883, @aleksandr.urakov wrote:

I've checked your solution, and it's worked for me too! I think that your solution is better because it is more straight-forward. Here is the updated patch.

It also has a higher chance of behaving identically on different systems.

[aleksandr.urakov]

Zachary, can you take a look? please?

lit/helper/build.py

def _get_visual_studio_environment(self):
         includes = vcincludes + sdkincludes
         libs = vclibs + sdklibs
         libs = [os.path.join(x, self.msvc_arch_str) for x in libs]
         compileenv = None
         linkenv = None
         defaultenv = {}
         if sys.platform == 'win32':
             defaultenv = { x : os.environ[x] for x in
-                          ['SystemDrive', 'SystemRoot', 'TMP', 'TEMP'] }
+                          ['SystemDrive', 'SystemRoot', 'TMP', 'TEMP', 'VCINSTALLDIR'] }
             # The directory to mspdbcore.dll needs to be in PATH, but this is
             # always in the native toolchain path, not the cross-toolchain
             # path.  So, for example, if we're using HostX64\x86 then we need
             # to add HostX64\x64 to the path, and if we're using HostX86\x64
             # then we need to add HostX86\x86 to the path.
             if self.toolchain_type == 'msvc':
                 defaultenv['PATH'] = self._get_msvc_native_toolchain_dir()