[X86] Create extra prolog/epilog for stack realignment

The base pointer register is reserved by compiler when there is
dynamic size alloca and stack realign in a function. However the
base pointer register is not defined in X86 ABI, so user can use
this register in inline assembly. The inline assembly would
clobber base pointer register without being awared by user. This
patch is to create extra prolog to save the stack pointer to a
scratch register and use this register to reference argument from
stack. For some calling convention (e.g. regcall), there may be
few scratch register.
Below is the example code for such case.

```
extern int bar(void *p);
long long foo(size_t size, char c, int id) {
  __attribute__((__aligned__(64))) int a;
  char *p = (char *)alloca(size);
  asm volatile ("nop"::"S"(405):);
  asm volatile ("movl %0, %1"::"r"(id), "m"(a):);
  p[2] = 8;
  memset(p, c, size);
  return bar(p);
}
```
And below prolog/epilog will be emit for this case.
```
leal    4(%esp), %ebx
.cfi_def_cfa %ebx, 0
andl    $-128, %esp
pushl   -4(%ebx)
...
leal    4(%ebx), %esp
.cfi_def_cfa %esp, 4
```

Differential Revision: https://reviews.llvm.org/D145650