objtool: Change "warning:" to "error:" for --Werror

This is similar to GCC's behavior and makes it more obvious why the
build failed.

Suggested-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Brendan Jackman <jackmanb@google.com>
Link: https://lore.kernel.org/r/56f0565b15b4b4caa9a08953fa9c679dfa973514.1741975349.git.jpoimboe@kernel.org

Author: jpoimboe

tools/objtool/include/objtool/warn.h

@@ -43,8 +43,10 @@ static inline char *offstr(struct section *sec, unsigned long offset)
 
 #define WARN(format, ...)				\
 	fprintf(stderr,					\
-		"%s: warning: objtool: " format "\n",	\
-		objname, ##__VA_ARGS__)
+		"%s: %s: objtool: " format "\n",	\
+		objname,				\
+		opts.werror ? "error" : "warning",	\
+		##__VA_ARGS__)
 
 #define WARN_FUNC(format, sec, offset, ...)		\
 ({							\