Fix the path for installing GTK3 libraries.

Second attempt because GTK3_LIBDIR already contains GTK3_PREFIX.

Signed-off-by: Slávek Banko <slavek.banko@axis.cz>
(cherry picked from commit 490572625b)

tdegtk/Makefile.am

@@ -36,7 +36,7 @@ source_c = \
 	$(srcdir)/tdegtk-baseengine.cpp \
 	$(srcdir)/tdegtk-theme.cpp
 
-enginedir = $(GTK3_PREFIX)/$(GTK3_LIBDIR)/gtk-3.0/$(GTK3_VERSION)/theming-engines
+enginedir = $(GTK3_LIBDIR)/gtk-3.0/$(GTK3_VERSION)/theming-engines
 engine_LTLIBRARIES = libtdegtk.la
 
 libtdegtk_la_SOURCES = $(source_h) $(source_c)