baremetal: build userland/ programs using baremetal path property instead of symlinks

Otherwise I'll go crazy with symlink action.

baremetal/lib/aarch64.S

@@ -1,7 +1,7 @@
 #include <lkmc.h>
 
-.global mystart
-mystart:
+.global lkmc_start
+lkmc_start:
     /* = NEON setup */
     mov x1, #(0x3 << 20)
     msr cpacr_el1, x1
@@ -20,6 +20,7 @@ mystart:
     bl on_exit
 
     /* Run main. */
+    mov x0, 0
     bl main
 
     /* If main returns, exit. */

baremetal/lib/arm.S

@@ -1,7 +1,7 @@
 #include <lkmc.h>
 
-.global mystart
-mystart:
+.global lkmc_start
+lkmc_start:
     /* Prepare the stack for main, mandatory for C code. */
     ldr sp, =stack_top
 
@@ -10,6 +10,7 @@ mystart:
     bl on_exit
 
     /* Run main. */
+    mov r0, 0
     bl main
 
     /* If main returns, exit. */

baremetal/lib/syscalls.c

@@ -5,6 +5,13 @@
 #include <lkmc.h>
 #include <lkmc/m5ops.h>
 
+void lkmc_baremetal_on_exit_callback(int status, void *arg) {
+    (void)arg;
+    if (status != 0) {
+        printf("lkmc_exit_status_%d\n", status);
+    }
+}
+
 enum {
     UART_FR_RXFE = 0x10,
 };