[lldb] Propagate XDG_CACHE_HOME environment variable to tests

This variable is used to reducing the likelihood of hitting module cache
issues in CI where different branches can potentially run on the same
machine.

lldb/test/API/lit.cfg.py

@@ -129,11 +129,6 @@ if is_configured('shared_libs'):
     lit_config.warning("unable to inject shared library path on '{}'".format(
         platform.system()))
 
-# Propagate LLDB_CAPTURE_REPRODUCER
-if 'LLDB_CAPTURE_REPRODUCER' in os.environ:
-  config.environment['LLDB_CAPTURE_REPRODUCER'] = os.environ[
-      'LLDB_CAPTURE_REPRODUCER']
-
 # Support running the test suite under the lldb-repro wrapper. This makes it
 # possible to capture a test suite run and then rerun all the test from the
 # just captured reproducer.
@@ -256,3 +251,12 @@ config.test_format = lldbtest.LLDBTest(dotest_cmd)
 if 'FREEBSD_LEGACY_PLUGIN' in os.environ:
   config.environment['FREEBSD_LEGACY_PLUGIN'] = os.environ[
       'FREEBSD_LEGACY_PLUGIN']
+
+# Propagate LLDB_CAPTURE_REPRODUCER
+if 'LLDB_CAPTURE_REPRODUCER' in os.environ:
+  config.environment['LLDB_CAPTURE_REPRODUCER'] = os.environ[
+      'LLDB_CAPTURE_REPRODUCER']
+
+# Propagate XDG_CACHE_HOME
+if 'XDG_CACHE_HOME' in os.environ:
+  config.environment['XDG_CACHE_HOME'] = os.environ['XDG_CACHE_HOME']

lldb/test/Shell/lit.cfg.py

@@ -45,6 +45,7 @@ llvm_config.with_system_environment([
     'LLDB_CAPTURE_REPRODUCER',
     'TEMP',
     'TMP',
+    'XDG_CACHE_HOME',
 ])
 
 # Support running the test suite under the lldb-repro wrapper. This makes it

lldb/test/Unit/lit.cfg.py

@@ -28,6 +28,7 @@ llvm_config.with_system_environment([
     'PATH',
     'TEMP',
     'TMP',
+    'XDG_CACHE_HOME',
 ])
 llvm_config.with_environment('PATH',
                              os.path.dirname(sys.executable),