In addition to use ${srcdir} and deliver ${NOTMUCH_SRCDIR} where needed,
source from ruby bindings had to be copied to the out-of-tree target
directory -- if the source files in source directory were referenced
in build and there were also built object files there, those could have
been considered as target files (and then not found when attempting
to create bindings/ruby/notmuch.so).
This is supposed to help build on systems like MacOS with different
conventions for naming shared libraries. We have already computed the
relevant names, so doing it again in ruby seems like a bad idea.
Currently it simply finds any library available, and if notmuch is
installed in the system, it would give priority to that library.
Let's implement our own helper functions to link directly to the local
library, and give priority to the local header file.
Also, add an option to properly check if there are missing symbols.
Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>