GDB 7.4 --with-python doesn't like d:/foo/bar

[Eli Zaretskii <eliz@gnu.org>]

GDB 7.4 cannot be configured using --with-python-d:/foo/bar on
MS-Windows.  The gdb/configure script aborts with an error message:

  checking whether to use python... d:/usr/python26
  configure: error: invalid value for --with-python

The culprit is this snippet from gdb/configure.ac:

  if test "${with_python}" = no; then
    AC_MSG_WARN([python support disabled; some features may be unavailable.])
    have_libpython=no
  else
    case "${with_python}" in
    /*)   <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
      if test -d ${with_python}; then
	# Assume the python binary is ${with_python}/bin/python.
	python_prog="${with_python}/bin/python"
	python_prefix=
	# If python does not exit ${with_python}/bin, then try in
	# ${with_python}.  On Windows/MinGW, this is where the Python
	# executable is.
	if test ! -x "${python_prog}"; then
	  python_prog="${with_python}/python"
	  python_prefix=
	fi
	if test ! -x "${python_prog}"; then
	  # Fall back to gdb 7.0/7.1 behaviour.
	  python_prog=missing
	  python_prefix=${with_python}
	fi
      elif test -x "${with_python}"; then
	# While we can't run python compiled for $host (unless host == build),
	# the user could write a script that provides the needed information,
	# so we support that.
	python_prog=${with_python}
	python_prefix=
      else
	AC_ERROR(invalid value for --with-python)
      fi
      ;;

As can be clearly seen, it only accepts absolute file names that begin
with a forward slash.

I don't have Autoconf installed on the Windows/MinGW machine where I
did this (thus no patch), so I manually edited gdb/configure to
replace the line marked above with

 [\\/]* | [A-Za-z]:[\\/]*)

Then the configure and build steps ran successfully to completion.

Since (AFAIK) [] is a quote sequence in Autoconf, could someone please
make the appropriate change in configure.ac to fix this?

TIA