Revert "Revert "Lose the hand-written futex assembler.""

The problem with the original patch was that using syscall(3) means that
errno can be set, but pthread_create(3) was abusing the TLS errno slot as
a pthread_mutex_t for the thread startup handshake.

There was also a mistake in the check for syscall failures --- it should
have checked against -1 instead of 0 (not just because that's the default
idiom, but also here because futex(2) can legitimately return values > 0).

This patch stops abusing the TLS errno slot and adds a pthread_mutex_t to
pthread_internal_t instead. (Note that for LP64 sizeof(pthread_mutex_t) >
sizeof(uintptr_t), so we could potentially clobber other TLS slots too.)

I've also rewritten the LP32 compatibility stubs to directly reuse the
code from the .h file.

This reverts commit 75c55ff84e.

Bug: 15195455
Change-Id: I6ffb13e5cf6a35d8f59f692d94192aae9ab4593d

libc/arch-x86/bionic/futex_x86.S

@@ -1,16 +0,0 @@
-#include <private/bionic_asm.h>
-
-// int __futex_syscall4(volatile void* ftx, int op, int val, const struct timespec* timeout)
-ENTRY_PRIVATE(__futex_syscall4)
-    pushl   %ebx
-    pushl   %esi
-    movl    12(%esp), %ebx      /* ftx */
-    movl    16(%esp), %ecx      /* op */
-    movl    20(%esp), %edx      /* val */
-    movl    24(%esp), %esi      /* timeout */
-    movl    $__NR_futex, %eax
-    int     $0x80
-    popl    %esi
-    popl    %ebx
-    ret
-END(__futex_syscall4)

libc/arch-x86/syscalls/futex.S

@@ -1,42 +0,0 @@
-/* Generated by gensyscalls.py. Do not edit. */
-
-#include <private/bionic_asm.h>
-
-ENTRY(futex)
-    pushl   %ebx
-    pushl   %ecx
-    pushl   %edx
-    pushl   %esi
-    pushl   %edi
-    pushl   %ebp
-    .cfi_def_cfa_offset 24
-    .cfi_rel_offset ebx, 0
-    .cfi_rel_offset ecx, 4
-    .cfi_rel_offset edx, 8
-    .cfi_rel_offset esi, 12
-    .cfi_rel_offset edi, 16
-    .cfi_rel_offset ebp, 20
-    mov     28(%esp), %ebx
-    mov     32(%esp), %ecx
-    mov     36(%esp), %edx
-    mov     40(%esp), %esi
-    mov     44(%esp), %edi
-    mov     48(%esp), %ebp
-    movl    $__NR_futex, %eax
-    int     $0x80
-    cmpl    $-MAX_ERRNO, %eax
-    jb      1f
-    negl    %eax
-    pushl   %eax
-    call    __set_errno
-    addl    $4, %esp
-    orl     $-1, %eax
-1:
-    popl    %ebp
-    popl    %edi
-    popl    %esi
-    popl    %edx
-    popl    %ecx
-    popl    %ebx
-    ret
-END(futex)

libc/arch-x86/x86.mk

@@ -23,7 +23,6 @@ libc_bionic_src_files_x86 := \
 libc_bionic_src_files_x86 += \
     arch-x86/bionic/__bionic_clone.S \
     arch-x86/bionic/_exit_with_stack_teardown.S \
-    arch-x86/bionic/futex_x86.S \
     arch-x86/bionic/__get_sp.S \
     arch-x86/bionic/_setjmp.S \
     arch-x86/bionic/setjmp.S \