Add abort () to jerry-libc

Added declaration and implementations of `void abort (void)` to
jerry-libc. As the linux implementation relies on the `getpid`
syscall - which has no arguments - `syscall_0` implementations
have been added as well.

`libc_fatal` has been adapted to use the new `abort` function
instead of `exit`. This also made the definition of
`LIBC_FATAL_ERROR_EXIT_CODE` unnecessary.

Finally, the syscall fatal error message was fixed.

JerryScript-DCO-1.0-Signed-off-by: Akos Kiss akiss@inf.u-szeged.hu

jerry-libc/target/mcu-stubs/jerry-libc-target.c

@@ -38,6 +38,15 @@ exit (int status __attr_unused___)
   }
 } /* exit */
 
+/** abort - cause abnormal process termination  */
+void __attr_noreturn___ __attr_used___
+abort (void)
+{
+  while (true)
+  {
+  }
+} /* abort */
+
 /**
  * fwrite
  *