set -x
./configure >log
grep libdir_QUOTED config.log
./configure --prefix=/foo >log
grep libdir_QUOTED config.log
./configure --exec-prefix=/bar >log
grep libdir_QUOTED config.log
./configure --prefix=/foo --exec-prefix=/bar >log
grep libdir_QUOTED config.log
./configure --prefix=/foo --exec_prefix=/bar --libdir=/foo/lib64 >log
grep libdir_QUOTED config.log