Allow parallelizing bdlib/libelf builds

lib/Makefile.in

@@ -8,7 +8,7 @@ VPATH = @srcdir@
 
 #include $(top_srcdir)/build/build.mk
 
-.PHONY: default clean distclean normal debug general buildcheck notice notice_debug build units libelf libelf_notice
+.PHONY: default clean distclean normal debug general buildcheck notice notice_debug build units libelf libelf_notice bdlib
 
 default: normal
 
@@ -41,13 +41,13 @@ $(top_srcdir)/lib/libelf/lib/libelf.a: libelf_notice
 
 libelf: @LIBELF_BUNDLED@
 
-build:
+$(top_srcdir)/lib/bdlib/src/libbdlib.a:
 	+@cd bdlib && $(MAKE) bdlib
-	+@$(MAKE) libelf
 
-build.debug:
-	+@cd bdlib && $(MAKE) debug
-	+@$(MAKE) libelf
+bdlib: $(top_srcdir)/lib/bdlib/src/libbdlib.a
+
+build: $(top_srcdir)/lib/bdlib/src/libbdlib.a @LIBELF_BUNDLED@
+build.debug: $(top_srcdir)/lib/bdlib/src/libbdlib.a @LIBELF_BUNDLED@
 
 buildcheck: build