Force libhamlib to be relinked when a backend is updated

Add the rig and rotor backends to the list of dependencies for
libhamlib.la so that updating a given backend will force libhamlib.la to
be relinked as well.  Thanks to Bill Sommerville, G4WJS, for reporting
this.

Removed obsolete references and variables related to LTDL.

src/Makefile.am

@@ -1,8 +1,5 @@
 # src/Makefile.am
 
-# $(LTDLINCL) is set by LTDL_INIT macro in configure.ac
-AM_CPPFLAGS = @AM_CPPFLAGS@ $(LTDLINCL)
-
 RIGSRC = rig.c serial.c serial.h misc.c misc.h register.c register.h event.c \
 	event.h cal.c cal.h conf.c tones.c tones.h rotator.c locator.c rot_reg.c \
 	rot_conf.c rot_conf.h iofunc.c iofunc.h ext.c mem.c settings.c \
@@ -12,13 +9,11 @@ RIGSRC = rig.c serial.c serial.h misc.c misc.h register.c register.h event.c \
 lib_LTLIBRARIES = libhamlib.la
 libhamlib_la_SOURCES = $(RIGSRC)
 libhamlib_la_LDFLAGS = $(WINLDFLAGS) $(OSXLDFLAGS) -no-undefined -version-info @ABI_VERSION@:@ABI_REVISION@:@ABI_AGE@
-# libhamlib_la_CFLAGS = -DIN_HAMLIB $(AM_CFLAGS) -DHAMLIB_MODULE_DIR=\"$(pkglibdir)\"
 
-# $(LIBLTDL) is set by LTDL_INIT macro
-libhamlib_la_LIBADD = $(LIBLTDL) $(top_builddir)/lib/libmisc.la \
+libhamlib_la_LIBADD = $(top_builddir)/lib/libmisc.la \
 		      @BACKENDEPS@ @ROT_BACKENDEPS@ \
 		      @NET_LIBS@ @MATH_LIBS@ $(LIBUSB_LIBS)
 
-libhamlib_la_DEPENDENCIES = $(LTDLDEPS) $(top_builddir)/lib/libmisc.la
+libhamlib_la_DEPENDENCIES = $(top_builddir)/lib/libmisc.la @BACKENDEPS@ @ROT_BACKENDEPS@
 
 EXTRA_DIST = Android.mk