simplify and fix CFLAGS for no blobdigest vmod

src/Makefile.am

@@ -19,7 +19,7 @@ vmod_blob.h: vmod_get_h $(VMOD_BLOB)
 vmod_blobdigest.h: vmod_get_h $(VMOD_BLOBDIGEST)
 	$(builddir)/vmod_get_h blobdigest $(VMOD_BLOBDIGEST) >$@
 tus_blob.c: vmod_blob.h  vmod_blobdigest.h
-libvmod_tus_la_CFLAGS = $(AM_CFLAGS) -DHAVE_CHKSUM=1
+AM_CFLAGS += -DHAVE_CHKSUM=1
 endif
 
 # ----------------------------------------
@@ -28,7 +28,6 @@ endif
 vmod_LTLIBRARIES = \
 	libvmod_tus.la
 
-libvmod_tus_la_LDFLAGS = $(VMOD_LDFLAGS)
 libvmod_tus_la_SOURCES = \
 	tbl_hash_enum.h \
 	tbl_method.h \