[lldb] Fix SBFileSpec.fullpath for Windows

Fix `fullpath` to not assume a `/` path separator. This was discovered when
D133130 failed on Windows. Use `os.path.join()` to fix the issue.

Reviewed By: mib

Differential Revision: https://reviews.llvm.org/D133366

lldb/bindings/interface/SBFileSpec.i

@@ -88,7 +88,7 @@ public:
             spec_dir = self.GetDirectory()
             spec_file = self.GetFilename()
             if spec_dir and spec_file:
-                return '%s/%s' % (spec_dir, spec_file)
+                return os.path.join(spec_dir, spec_file)
             elif spec_dir:
                 return spec_dir
             elif spec_file:

lldb/test/API/python_api/file_spec/TestFileSpecAPI.py

@@ -0,0 +1,15 @@
+import lldb
+import os
+from lldbsuite.test.decorators import *
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test import lldbutil
+
+
+class TestCase(TestBase):
+    NO_DEBUG_INFO_TESTCASE = True
+
+    def test_full_path(self):
+        file_spec = lldb.SBFileSpec()
+        file_spec.SetDirectory("a")
+        file_spec.SetFilename("b")
+        self.assertEqual(file_spec.fullpath, os.path.join("a", "b"))