libsynthesissdk calls libsmltk directly (in san.cpp). libsmltk used to
be provided via libsynthesis, but only if really linked (not always
the case, for example when using the SDK in "open engine dynamically"
mode) and indirect linking stopped working with more recent Linux
bintools which enforce that all libraries are properly declared.

This patch fixes this both in libtool linking (.la files, LIBADD) and
pkg-config definition files (.pc files).