configure.ac: respect 'g' variants of libtool/libtoolize

BSD OS'es (OS X for me) provide GNU tools with prefixed 'g'. To find correct
versions of libtool/libtoolize on those systems search also for
glibtool/glibtoolize.

Signed-off-by: Andreas Bießmann <andreas@biessmann.de>
Signed-off-by: Bryan Hundven <bryanhundven@gmail.com>
[yann.morin.1998@free.fr: search for the g-variant first]
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Message-Id: <2f1530b54afcb6a00e1d.1395158786@andreas-mbp.er.biessmann.org>
Patchwork-Id: 331467

 diff -ru ltrace-0.5.3.org/configure ltrace-0.5.3/configure

 --- ltrace-0.5.3.org/configure	2011-08-21 18:55:15.000000000 +0200

 +++ ltrace-0.5.3/configure	2011-08-21 18:54:46.000000000 +0200

 @@ -15,8 +15,12 @@

  echo $PACKAGE_VERSION

  echo -n "checking HOST_OS... "

 -HOST_OS=$( uname -s )

 -if [ "$HOST_OS" = "Linux" ]

 +if [ -z "$HOST_OS" ] ; then

 +  HOST_OS=$( uname -s )

 +else

 +  echo -n "using preset: "

 +fi

 +if [ "$HOST_OS" = "Linux" -o "$HOST_OS" = "linux" ]

  then

    HOST_OS="linux-gnu"

  fi