add distinct build target definitions for gmp, mpfr, and mpc.

Generated from within gcc, the above dependency libraries are built with the
--disable-shared libtool option. As with binutils, distinct build steps for
each of the above in litecross/Makefile allow for their correct (static only)
generation by an alternate libtool utility, such as slibtool.

litecross/Makefile

@@ -214,7 +214,19 @@ obj_gcc/.lc_configured: | obj_gcc src_gcc
 	cd obj_gcc && ../src_gcc/configure $(FULL_GCC_CONFIG)
 	touch $@
 
-obj_gcc/gcc/.lc_built: | obj_gcc/.lc_configured
+obj_gcc/.lc_gmp_built: | obj_gcc/.lc_configured
+	cd obj_gcc && $(MAKE) MAKE="$(MAKE) $(LIBTOOL_STATIC_ARG)" all-gmp
+	touch $@
+
+obj_gcc/.lc_mpfr_built: | obj_gcc/.lc_gmp_built
+	cd obj_gcc && $(MAKE) MAKE="$(MAKE) $(LIBTOOL_STATIC_ARG)" all-mpfr
+	touch $@
+
+obj_gcc/.lc_mpc_built: | obj_gcc/.lc_mpfr_built
+	cd obj_gcc && $(MAKE) MAKE="$(MAKE) $(LIBTOOL_STATIC_ARG)" all-mpc
+	touch $@
+
+obj_gcc/gcc/.lc_built: | obj_gcc/.lc_mpc_built
 	cd obj_gcc && $(MAKE) MAKE="$(MAKE) $(LIBTOOL_ARG)" all-gcc
 	touch $@