configure --with-glibc-be-dir override is silently ignored

[SamHerts]

Bug:

The --with-glibc-be-dir=DIR configure option is documented as the supported method for specifying a non-standard back-end glibc path on heterogeneous clusters.

The option is silently ignored at configure time due to an argument-processing ordering bug.

Detection block:

Spindle/configure.common.ac

Lines 374 to 379 in ba9bbcc

	if test "x$GLIBC_BE_DIR" = "x"; then
	# Get glibc location on front-end
	CAT=`which cat`
	LIBC_FILE=`ldd $CAT | grep libc | awk -F ' ' '{print $3}'`
	GLIBC_BE_DIR=`dirname $LIBC_FILE`
	fi

But argument parsing happens 40 lines later and GLIBC_BE_DIR is already set, so the assignment GLIBC_BE_DIR=${withval} has no effect

Spindle/configure.common.ac

Lines 416 to 418 in ba9bbcc

	AC_ARG_WITH(glibc-be-dir,
	[AS_HELP_STRING([--with-glibc-be-dir=DIR],[If glibc on compute nodes is installed in a non-standard location, then DIR is the directory containing libc.so.6])],
	[GLIBC_BE_DIR=${withval}])

Steps to recreate:

cd containers/spindle-serial-ubuntu
docker compose build
docker compose up -d
docker exec spindlenode grep 'GLIBC_BE_DIR' /home/spindleuser/Spindle-build/src/client/Makefile

GLIBC_BE_DIR = /lib/aarch64-linux-gnu

Reconfigure with glibc being set to a false path:

docker exec spindlenode bash -c '
    cd ~/Spindle-build
    ../../Spindle/configure \
      --prefix=~/Spindle-inst \
      --enable-sec-munge \
      --with-rm=serial \
      --with-localstorage=/tmp \
      --with-glibc-be-dir=/definitely/not/real \
    2>&1 | grep -i glibc
  '
docker exec spindlenode grep 'GLIBC_BE_DIR' /home/spindleuser/Spindle-build/src/client/Makefile

GLIBC_BE_DIR = /lib/aarch64-linux-gnu

Fix:

Move AC_ARG_WITH(glibc-be-dir, ...) before the detection block so the if test "x$GLIBC_BE_DIR" = "x" guard correctly short-circuits when a user provides an explicit path.