Change startup ABI for untrusted code to be C-compatible

src/untrusted/stubs/crt1_x86_64.S

Index: src/untrusted/stubs/crt1_x86_64.S
diff --git a/src/untrusted/stubs/crt1_x86_64.S b/src/untrusted/stubs/crt1_x86_64.S
deleted file mode 100644
index f3044fcb46c54fb0655b328c2238506ad0df23f0..0000000000000000000000000000000000000000
--- a/src/untrusted/stubs/crt1_x86_64.S
+++ /dev/null
@@ -1,84 +0,0 @@
-/*
- * Copyright 2010 The Native Client Authors. All rights reserved.
- * Use of this source code is governed by a BSD-style license that can
- * be found in the LICENSE file.
- */
-
-/* Native Client crt0 startup code for x86-64*/
-
-    .text
-    .p2align NACLENTRYALIGN,0xf4
-
-    .global _start
-_start:
-    /*
-     *  The i386 ELF ABI specifies that on entry the stack looks like:
-     *            --------------------------------
-     *            |          Unspecified         |
-     *            --------------------------------
-     *            | Information block, including |
-     *            |       argument strings,      |
-     *            |      environment strings,    |
-     *            |     auxiliary information    |
-     *            |              ...             |
-     *            |        (size varies)         |
-     *            --------------------------------
-     *            |         Unspecified          |
-     *            --------------------------------
-     *            | Null auxiliary vector entry  |
-     *            --------------------------------
-     *            |        Auxiliary vector      |
-     *            |              ...             |
-     *            |        (2-word entries)      |
-     *            --------------------------------
-     *            |            0 word            |
-     *            --------------------------------
-     *            |      Environment pointers    |
-     *            |              ...             |
-     *            |         (one word each)      |
-     *            --------------------------------
-     *            |       Argument pointers      |
-     *            |              ...             |
-     *  4(%esp)   |    (Argument count words)    |
-     *            --------------------------------
-     *  0(%esp)   |        Argument count        |
-     *            --------------------------------
-     *            |           Undefined          |
-     *            --------------------------------
-     *  TODO(sehr): fix stack alignments of atexit, _init, _fini, and
-     *              exit.
-     */
-
-    /*
-     *  Because we are going to align the stack 0mod16 for SSE2,
-     *  We need to gather the argc, argv, and envp pointers before
-     *  moving esp.
-     */
-    popq    %rsi               /* Remove argc from the top of the stack */
-    movq    %rsp, %rcx         /* Save the argv pointer */
-
-    /*
-     * Finding envp requires skipping over argc+1 words.
-     */
-
-    /* NOTE(khim): we are using ILP32 model in x86-64 mode! */
-    leal    4(%rsp, %rsi, 4), %ebx
-
-    /*
-     * Align the stack 0mod16, for SSE2
-     */
-    andq    $0xfffffffffffffff0, %rsp
-
-    /*
-     *Save the arguments in spare registers.
-     */
-    movq    %rsi, %rdi
-    movq    %rcx, %rsi
-    movl    %ebx, %edx
-    naclcall __nacl_startup
-
-halt_loop:
-    hlt
-    jmp     halt_loop
-    .p2align 5
-