Remove -Werror option.

Although it makes impossible to ignore errors, it also makes impossible
to use older code with newer compiler versions, which tend to rant more
with age.

Reviewed-by: Kurt Daverman <krd@vmware.com>

lib/Makefile.rules

@@ -21,7 +21,7 @@ CFLAGS := -m32 -ffreestanding -nostdinc -fno-stack-protector
 LDFLAGS := -nostdlib -Wl,-T,$(LIB_DIR)/metalkit/image.ld
 
 # Extra warnings
-CFLAGS += -Wall -Werror
+CFLAGS += -Wall
 
 # Size Optimizations.
 CFLAGS += -Os -fweb