gh-98401: Invalid escape sequences emits SyntaxWarning (#99011)

A backslash-character pair that is not a valid escape sequence now
generates a SyntaxWarning, instead of DeprecationWarning.  For
example, re.compile("\d+\.\d+") now emits a SyntaxWarning ("\d" is an
invalid escape sequence), use raw strings for regular expression:
re.compile(r"\d+\.\d+"). In a future Python version, SyntaxError will
eventually be raised, instead of SyntaxWarning.

Octal escapes with value larger than 0o377 (ex: "\477"), deprecated
in Python 3.11, now produce a SyntaxWarning, instead of
DeprecationWarning. In a future Python version they will be
eventually a SyntaxError.

codecs.escape_decode() and codecs.unicode_escape_decode() are left
unchanged: they still emit DeprecationWarning.

* The parser only emits SyntaxWarning for Python 3.12 (feature
  version), and still emits DeprecationWarning on older Python
  versions.
* Fix SyntaxWarning by using raw strings in Tools/c-analyzer/ and
  wasm_build.py.

Tools/c-analyzer/c_parser/_state_machine.py

@@ -96,7 +96,7 @@ def parse(srclines):
 #    # end matched parens
 #    ''')
 
-'''
+r'''
         # for loop
         (?:
             \s* \b for

Tools/wasm/wasm_build.py

@@ -137,7 +137,7 @@ def read_python_version(configure: pathlib.Path = CONFIGURE) -> str:
     configure and configure.ac are the canonical source for major and
     minor version number.
     """
-    version_re = re.compile("^PACKAGE_VERSION='(\d\.\d+)'")
+    version_re = re.compile(r"^PACKAGE_VERSION='(\d\.\d+)'")
     with configure.open(encoding="utf-8") as f:
         for line in f:
             mo = version_re.match(line)