user: implement mlibc as the libc, finally.

It's finally done..

Signed-off-by: kaguya <vpshinomiya@protonmail.com>

user/include/mlibc/sysdeps/linux/x86_64/thread_entry.S

@@ -0,0 +1,26 @@
+#include "mlibc-asm/helpers.h"
+#include "syscallnos.h"
+
+.section .text
+
+PROC_START(__mlibc_spawn_thread)
+	xor %eax, %eax
+	/* The rest of the args are already in the right registers,
+	* only need to fixup rcx to r10
+	*/
+	mov %rcx, %r10
+	mov $__NR_clone, %rax
+	syscall
+	test %eax, %eax
+	jnz 1f
+	xor %ebp, %ebp
+	pop %rdi
+	pop %rsi
+	call __mlibc_enter_thread
+	hlt
+1:
+	ret
+PROC_END(__mlibc_spawn_thread)
+
+GNU_STACK_NOTE()
+