buildsys: make deb: use --lib for first pass build

since it'll rebuild the lib & binaries anyway after the
copy, only build the library (to get the dependencies out of
the way), but dont build the binaries...

saves a couple seconds of build time

Signed-off-by: Wolfgang Bumiller <w.bumiller@proxmox.com>

Makefile

@@ -57,7 +57,7 @@ doc:
 .PHONY: build
 build:
 	rm -rf build
-	cargo build --release
+	cargo build --release --lib
 	rsync -a debian Makefile defines.mk Cargo.toml Cargo.lock \
 	    src zstd-sys $(SUBDIRS) \
 	    target tests build/