[LIT] Add win32 PLATFORM env var to test config

[omjavaid]

Summary

LIT skips various system environment variables while building test
config. It turns out that we require PLATFORM environment variable for
detection of x86 vs Arm windows platform.

This patch adds system environment variable PLATFORM into LIT test
config for detection of win32 Arm platform.

[mstorsjo]

LGTM

lldb/test/Shell/helper/build.py

def build_commands(self):
             commands.append(self._get_link_command())
         return commands
 
 
 class MsvcBuilder(Builder):
     def __init__(self, toolchain_type, args):
         Builder.__init__(self, toolchain_type, args, '.obj')
 
+        if os.getenv('PLATFORM') == 'arm64':
+            self.msvc_arch_str = 'arm' if self.arch == '32' else 'arm64'
+        else:
             self.msvc_arch_str = 'x86' if self.arch == '32' else 'x64'
 
         if toolchain_type == 'msvc':
             # Make sure we're using the appropriate toolchain for the desired
             # target type.
             compiler_parent_dir = os.path.dirname(self.compiler)
             selected_target_version = os.path.basename(compiler_parent_dir)
             if selected_target_version != self.msvc_arch_str:
                 host_dir = os.path.dirname(compiler_parent_dir)

llvm/utils/lit/lit/llvm/config.py

def __init__(self, lit_config, config):
                                                 required_tools)
             if path is None:
                 path = self._find_git_windows_unix_tools(required_tools)
             if path is not None:
                 self.with_environment('PATH', path, append_path=True)
             # Many tools behave strangely if these environment variables aren't
             # set.
             self.with_system_environment(
-                ['SystemDrive', 'SystemRoot', 'TEMP', 'TMP'])
+                ['SystemDrive', 'SystemRoot', 'TEMP', 'TMP', 'PLATFORM'])
             self.use_lit_shell = True
 
             global lit_path_displayed
             if not self.lit_config.quiet and lit_path_displayed is False:
                 self.lit_config.note("using lit tools: {}".format(path))
                 lit_path_displayed = True
 
         # Choose between lit's internal shell pipeline runner and a real shell.