kbuild: rust: apply CONFIG_WERROR to hostprogs as well

Host programs should be (and currently are) warning-free. Apply
`CONFIG_WERROR` (i.e. `-Dwarnings`) to them as well, so that they are
kept that way.

Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Author: ojeda

Makefile

@@ -845,6 +845,9 @@ KBUILD_CFLAGS += $(stackp-flags-y)
 KBUILD_RUSTFLAGS-$(CONFIG_WERROR) += -Dwarnings
 KBUILD_RUSTFLAGS += $(KBUILD_RUSTFLAGS-y)
 
+KBUILD_HOSTRUSTFLAGS-$(CONFIG_WERROR) += -Dwarnings
+KBUILD_HOSTRUSTFLAGS += $(KBUILD_HOSTRUSTFLAGS-y)
+
 ifdef CONFIG_FRAME_POINTER
 KBUILD_CFLAGS	+= -fno-omit-frame-pointer -fno-optimize-sibling-calls
 KBUILD_RUSTFLAGS += -Cforce-frame-pointers=y