target: don't export local symbols

Symbols that are not used outside the file should not be exported
and should be declared as static.

Change-Id: Icbe7f7bce287b903edec9dc9db3370722c51fbd5
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/7173
Tested-by: jenkins
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>

src/target/mips_m4k.h

@@ -43,6 +43,5 @@ static inline void mips_m4k_isa_filter(enum mips32_isa_imp isa_imp, target_addr_
 		}
 	}
 }
-extern const struct command_registration mips_m4k_command_handlers[];
 
 #endif /* OPENOCD_TARGET_MIPS_M4K_H */