Avoid some shell calls in the build system

Avoid some shell calls in the build system
The DEP_INCLUDE_DIRS and DEP_LIB_DIRS variables always contain
single-quote dirs, so we can use e.g.
    $(subst $(space)',$(space)-L',$(space)$($1_$2_DEP_LIB_DIRS_SINGLE_QUOTED))
to add -L to the front of each dir. I've appended "_SINGLE_QUOTED" to
the variable names so we don't accidentally add bare directories to
them.