[lit] Repair tests for stdlib-only build

`config.host_triple` can be None when no host tools are built

This is based on 21d57e8 in main branch

test/lit.cfg

@@ -573,16 +573,18 @@ else:
         )
     )
     # Parse the host triple.
-    (host_cpu, host_vendor, host_os, host_vers) = re.match('([^-]+)-([^-]+)-([^0-9-]+)(.*)', config.host_triple).groups()
-    toolchain_lib_dir = make_path(config.swift_lib_dir, 'swift', host_os)
+    toolchain_lib_dir = None
+    if config.host_triple:
+        (host_cpu, host_vendor, host_os, host_vers) = re.match('([^-]+)-([^-]+)-([^0-9-]+)(.*)', config.host_triple).groups()
+        toolchain_lib_dir = make_path(config.swift_lib_dir, 'swift', host_os)
     config.host_build_swift = (
         "%s -target %s -g %s -I %s -L %s %s" % (
             config.swiftc_driver,
             config.host_triple,
             '' if kIsWindows else '-no-toolchain-stdlib-rpath',
             config.swift_build_lib_dir,
             config.swift_build_lib_dir,
-            '' if kIsWindows else '-Xlinker -rpath -Xlinker {}'.format(toolchain_lib_dir)
+            '' if kIsWindows or toolchain_lib_dir is None else '-Xlinker -rpath -Xlinker {}'.format(toolchain_lib_dir)
         )
     )