making the lalsuite:nightly container usable for building other containers

The lalsuite:nightly container includes the non-existent /builds directory in the output from pkg-config:

[jclark@balor] $ docker run -it containers.ligo.org/lscsoft/lalsuite:nightly
albert@bf1cc8660bd1:~$ pkg-config --cflags lal
-pthread -I/builds/lscsoft/lalsuite/opt/lalsuite/include 
albert@bf1cc8660bd1:~$ pkg-config --libs lal
-L/builds/lscsoft/lalsuite/opt/lalsuite/lib -llal -lgsl -lgslcblas -lm -lfftw3 -lfftw3f

This results in build errors for other software dependent on lal (i.e., bayeswave) which I am developing a container for.

A temporary workaround is to manually edit the pkg-config files like so:

RUN sed -i "s|/builds/lscsoft/lalsuite||g" ${PKG_CONFIG_PATH}/lal.pc