RTX - fix ARMv6 in premain (restore lr) and bx to main

Author: 0xc0170

libraries/rtos/rtx/TARGET_CORTEX_M/RTX_CM_lib.h

@@ -560,15 +560,18 @@ __attribute__((naked)) void pre_main (void) {
     ".syntax unified\n"
     ".thumb\n"
     /* Save link register (keep 8 byte alignment with dummy r4) */
-    "push    {r4, lr}\n"
+    "push    {r4, r5}\n"
+    "mov     r4, lr\n"
     "ldr  r0,= __libc_fini_array\n"
     "bl   atexit\n"
     "bl   __libc_init_array\n"
     /* Restore link register and branch so when main returns it
     * goes to the thread destroy function.
     */
-    "pop     {r4, lr}\n"
-    "b    main\n"
+    "mov     lr, r4\n"
+    "pop     {r4, r5}\n"
+    "ldr     r0,=main\n"
+    "bx      r0\n"
   );
 }