fix some -Wmissing-prototypes warnings

components/libc/compilers/armlibc/syscalls.c

@@ -25,6 +25,7 @@
 #ifdef RT_USING_POSIX_STDIO
 #include <posix/stdio.h>
 #endif /* RT_USING_POSIX_STDIO */
+#include <posix/stdlib.h>
 
 #define DBG_TAG    "armlibc.syscalls"
 #define DBG_LVL    DBG_INFO
@@ -312,7 +313,6 @@ void _ttywrch(int ch)
 /* for exit() and abort() */
 rt_weak void _sys_exit(int return_code)
 {
-    extern void __rt_libc_exit(int status);
     __rt_libc_exit(return_code);
     while (1);
 }

components/libc/compilers/common/cstdlib.c

@@ -9,6 +9,7 @@
  */
 
 #include <rtthread.h>
+#include <posix/stdlib.h>
 
 #define DBG_TAG    "stdlib"
 #define DBG_LVL    DBG_INFO

components/libc/compilers/common/include/posix/stdlib.h

@@ -18,6 +18,8 @@ extern "C" {
 #include <stdint.h>
 #include <stdlib.h>
 
+void __rt_libc_exit(int status);
+
 char *itoa(int n, char *buffer, int radix);
 char *lltoa(int64_t ll, char *buffer, int radix);
 char *ltoa(long l, char *buffer, int radix);

components/libc/compilers/dlib/syscalls.c

@@ -9,11 +9,11 @@
  */
 
 #include <rtthread.h>
+#include <posix/stdlib.h>
 
 /* for exit() and abort() */
 void __exit (int status)
 {
-    extern void __rt_libc_exit(int status);
     __rt_libc_exit(status);
     while(1);
 }

components/libc/compilers/newlib/syscalls.c

@@ -23,6 +23,7 @@
 #ifdef RT_USING_POSIX_STDIO
 #include <posix/stdio.h>
 #endif /* RT_USING_POSIX_STDIO */
+#include <posix/stdlib.h>
 #ifdef RT_USING_MODULE
 #include <dlmodule.h>
 #endif /* RT_USING_MODULE */
@@ -326,7 +327,6 @@ _ssize_t _write_r(struct _reent *ptr, int fd, const void *buf, size_t nbytes)
 /* for exit() and abort() */
 __attribute__ ((noreturn)) void _exit (int status)
 {
-    extern void __rt_libc_exit(int status);
     __rt_libc_exit(status);
     while(1);
 }

components/libc/compilers/picolibc/exit.c

@@ -9,11 +9,11 @@
 
 #include <rtthread.h>
 #include <sys/types.h>
+#include <posix/stdlib.h>
 
 /* for exit() and abort() */
 rt_noreturn void _exit (int status)
 {
-    extern void __rt_libc_exit(int status);
     __rt_libc_exit(status);
     while(1);
 }