To see what is really going on, we need to look at configure.in and Makefile.am in tandem.
In configure.in...
PKG_CHECK_MODULES(LIBGLADE, libxml-2.0 >= 2.4.10 atk >= 1.0.0 gtk+-2.0 >= 2.0.0) AC_SUBST(LIBGLADE_LIBS) AC_SUBST(LIBGLADE_CFLAGS) |
and in Makefile.am.
INCLUDES = @LIBGLADE_CFLAGS@ libglade_LDADD = @LIBGLADE_LIBS@ |
Since autoconf defines Makefile variables for each substitution that it does, the last example could also be written as
INCLUDES = $(LIBGLADE_CFLAGS) libglade_LDADD = $(LIBGLADE_LIBS) |