BaseTools: Fix Python SyntaxWarning

- Windows paths must be escaped
- Regex should use raw strings

Signed-off-by: Tim Crawford <tcrawford@system76.com>

BaseTools/Scripts/PatchCheck.py

@@ -237,7 +237,7 @@ class CommitMessageCheck:
             if sigtype == 'Cc' and len(sigs) == 0:
                 self.error('No Cc: tags for maintainers/reviewers found!')
 
-    cve_re = re.compile('CVE-[0-9]{4}-[0-9]{5}[^0-9]')
+    cve_re = re.compile(r'CVE-[0-9]{4}-[0-9]{5}[^0-9]')
 
     def check_overall_format(self):
         lines = self.msg.splitlines()