configure with relative srcdir causing absolute pathname in gcc/Makefile

[Doug Evans]

When you configure with a relative srcdir, as in

mkdir obj
cd obj
../src/configure blah

this is supposed to avoid absolute pathnames appearing in Makefiles.
This makes it easy to move the tree around.
[at least things used to work that way, dunno if this is a documented rule]

src/configure is breaking this for gcc_version_trigger

src/configure has this:

## the sed command below emulates the dirname command
topsrcdir=`cd \`echo ${progname} | sed -e 's,[^/]*$,,;s,/$,,;s,^$,.,'\`; ${PWDCMD-pwd}`

and this:

# Define the trigger file to make sure configure will re-run whenever
# the gcc version number changes.
if [ "${with_gcc_version_trigger+set}" = set ]; then
    gcc_version_trigger="$with_gcc_version_trigger"
    gcc_version=`grep version_string ${with_gcc_version_trigger} | sed -e 's/.*\"\([^ \"]*\)[ \"].*/\1/'`
else
    # If gcc's sources are available, define the trigger file.
    if [ -f ${topsrcdir}/gcc/version.c ] ; then
	gcc_version_trigger=${topsrcdir}/gcc/version.c
	gcc_version=`grep version_string ${gcc_version_trigger} | sed -e 's/.*\"\([^ \"]*\)[ \"].*/\1/'`
	case "$arguments" in
	  *--with-gcc-version-trigger=$gcc_version_trigger* )
	    ;;
	  * )
	    # Make sure configure.in knows about this.
	    arguments="--with-gcc-version-trigger=$gcc_version_trigger $arguments"
	    ;;
	esac
	withoptions="--with-gcc-version-trigger=$gcc_version_trigger $withoptions"
    fi
fi

thus causing the top level configure to pass

--with-gcc-version-trigger=/foo/bar/baz/gcc/version.c

to gcc's configure.