trace.c: mark a private file-scope symbol as static

Signed-off-by: Junio C Hamano <gitster@pobox.com>

cache.h

@@ -1205,7 +1205,6 @@ extern void alloc_report(void);
 /* trace.c */
 __attribute__((format (printf, 1, 2)))
 extern void trace_printf(const char *format, ...);
-extern void trace_vprintf(const char *key, const char *format, va_list ap);
 __attribute__((format (printf, 2, 3)))
 extern void trace_argv_printf(const char **argv, const char *format, ...);
 extern void trace_repo_setup(const char *prefix);

trace.c

@@ -62,7 +62,7 @@ static int get_trace_fd(const char *key, int *need_close)
 static const char err_msg[] = "Could not trace into fd given by "
 	"GIT_TRACE environment variable";
 
-void trace_vprintf(const char *key, const char *fmt, va_list ap)
+static void trace_vprintf(const char *key, const char *fmt, va_list ap)
 {
 	struct strbuf buf = STRBUF_INIT;