./configure/make in subdir?

[Phil Mayers]

Does anyone know if it's possible to persuade ./configure to work from 
within subdirs? I keep flipping back and forth between master and v2.1.x 
and it would be nice to be able to re-use builds without having to have 
two git repos & associated hassles.

I've seen syntax like this work on some projects.

git checkout v2.1.x
cd build-v21x
../configure --prefix=/opt/fr21x
make
make install

cd ..
git checkout master
cd master
../configure --prefix=/opt/frmaster
make
make install

...but this seems to fail on (the accursed!) libltdl subdir "configure" 
which is apparently jumping back up into the top-level source directory. 
I suspect it would similarly fail on the module configure scripts too.