Instead, it leaves it unexpeded as ${exec_prefix}/libexec, which is
unusable within C code. This has been explained very well here:
http://stackoverflow.com/questions/8264827/pass-directory-to-c-application-from-compilerThe workaround is cumbersome: it requires us to fiddle with CPPFLAGS in the Makefile. Seriously, this can't be a feature.
