[m-rev.] diff: escape square brackets in a configuration macro

[Julien Fischer]

Escape square brackets in a configuration macro.

m4/mercury.m4:
     As above.

Julien.

diff --git a/m4/mercury.m4 b/m4/mercury.m4
index a3c17cc..bf7a899 100644
--- a/m4/mercury.m4
+++ b/m4/mercury.m4
@@ -692,7 +692,7 @@ AC_REQUIRE([AC_PROG_CC])
  mercury_cv_gcc_version=`$CC -dumpversion | tr .- '  ' | {
      read major minor third ignore
      case $third in
-        [0-9]*)
+        [[0-9]]*)
              patchlevel=$third
              ;;
          *)