I'm building s6 from source on latest git tags and it seems to fail because
it cannot link execline:

./configure --disable-execline; make # works

./configure; make # fails with message
exec gcc -o s6-ftrig-listen -pipe -Wall -std=c99 -fno-exceptions
-fno-unwind-tables -fno-asynchronous-unwind-tables -Wa,--noexecstack
-ffunction-sections -fdata-sections -O2 -fomit-frame-pointer
-fno-stack-protector  -Wl,--sort-section=alignment -Wl,--sort-common
-Wl,--gc-sections src/pipe-tools/s6-ftrig-listen.o libs6.a.xyzzy -lexecline
-lskarnet
/home/linuxbrew/.linuxbrew/bin/ld: cannot find -lexecline
collect2: error: ld returned 1 exit status
make: *** [Makefile:138: s6-ftrig-listen] Error 1

Execline is installed and available.

$ ls /usr/lib/execline/
libexecline.a

Any clues about how to solve this?