[libc] Created syscall trampolines in libc

Using syscalls.inc (moved to src/include) generate trampoline functions
for directly calling syscalls with libc functions.

src/libraries/libc/include/j6libc/syscalls.h

@@ -0,0 +1,13 @@
+#pragma once
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#define SYSCALL(n, name, ...) j6_status_t _syscall_ ## name (__VA_ARGS__);
+#include "syscalls.inc"
+#undef SYSCALL
+
+#ifdef __cplusplus
+}
+#endif