problem with AH_TOP in autoconf 2.53

[Johan Danielsson]

There is a problem with 2.53 and constructs like this:

AH_TOP([char foo[] = "\123";])

The problem is that AS_LITERAL_IF is now using m4_bmatch instead of
m4_if/m4_bregex. What happens is the following:

AS_LITERAL_IF(73, [], [char foo...]) =>
m4_bmatch([73], [[`$]], [], [char foo...]) =>
m4_bmatch([73], [char foo...]) =>
m4_if([$#], 0, [],
      [$#], 1, [],
      [$#], 2, [],
      m4_bregexp([73], [char foo[] = "\123";]), -1, ...)

But because m4_if evaluates its arguments, the C-code gets parsed as a
regexp.

Solution: either make m4_bmatch handle this case (and possibly similar
ones), or revert to the old definition of LITERAL_IF.

/Johan