target: make local symbols static

Symbols that are not exported should be declared as static.

Change-Id: I2475524f4c14520e3163572560f4a9f276356ed5
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/7168
Tested-by: jenkins
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>

src/target/mem_ap.c

@@ -185,7 +185,7 @@ static struct reg_arch_type mem_ap_reg_arch_type = {
 	.set = mem_ap_reg_set,
 };
 
-const char *mem_ap_get_gdb_arch(struct target *target)
+static const char *mem_ap_get_gdb_arch(struct target *target)
 {
 	return "arm";
 }