gdbhooks: regex syntax error

Recent python complains about this pattern with
  SyntaxWarning: invalid escape sequence '\s'
because \s in a regular string just means 's'; for it to mean whitespace,
you need \\ or for the pattern to be a raw string.

Curiously, break-on-pass completion works for me either with or without this
change, but at least this avoids the warning.

gcc/ChangeLog:

	* gdbhooks.py: Fix regex syntax.

gcc/gdbhooks.py

@@ -642,7 +642,7 @@ class PassNames:
         self.names = []
         with open(os.path.join(srcdir, 'passes.def')) as f:
             for line in f:
-                m = re.match('\s*NEXT_PASS \(([^,]+).*\);', line)
+                m = re.match(r'\s*NEXT_PASS \(([^,]+).*\);', line)
                 if m:
                     self.names.append(m.group(1))