Subzero: Align the stack at the point of function calls.

tests_lit/llvm2ice_tests/ebp_args.ll

 ; This test originally exhibited a bug in ebp-based stack slots.  The
 ; problem was that during a function call push sequence, the esp
 ; adjustment was incorrectly added to the stack/frame offset for
 ; ebp-based frames.
 
 ; RUN: %llvm2ice -Om1 --target=x8632 --verbose none %s | FileCheck %s
 
 declare i32 @memcpy_helper2(i32 %buf, i32 %buf2, i32 %n);
 
 define i32 @memcpy_helper(i32 %buf, i32 %n) {
 entry:
   %n.arg_trunc = trunc i32 %n to i8
   %buf2 = alloca i8, i32 128, align 4
   %buf2.asint = ptrtoint i8* %buf2 to i32
   %arg_ext = zext i8 %n.arg_trunc to i32
   %call = call i32 @memcpy_helper2(i32 %buf, i32 %buf2.asint, i32 %arg_ext)
   ret i32 %call
 }
 
 ; This check sequence is highly specific to the current Om1 lowering
 ; and stack slot assignment code, and may need to be relaxed if the
 ; lowering code changes.
 
 ; CHECK: memcpy_helper:
-; CHECK: push     ebp
-; CHECK: mov      ebp, esp
-; CHECK: sub      esp, 20
-; CHECK: mov      eax, dword ptr [ebp+12]
-; CHECK: mov      dword ptr [ebp-4], eax
-; CHECK: sub      esp, 128
-; CHECK: mov      dword ptr [ebp-8], esp
-; CHECK: mov      eax, dword ptr [ebp-8]
-; CHECK: mov      dword ptr [ebp-12], eax
-; CHECK: movzx    eax, byte ptr [ebp-4]
-; CHECK: mov      dword ptr [ebp-16], eax
-; CHECK: push     dword ptr [ebp-16]
-; CHECK: push     dword ptr [ebp-12]
-; CHECK: push     dword ptr [ebp+8]
-; CHECK: call     memcpy_helper2
+; CHECK:  push     ebx
+; CHECK:  push     ebp
+; CHECK:  mov      ebp, esp
+; CHECK:  sub      esp, 20
+; CHECK:  mov      eax, dword ptr [ebp+16]
+; CHECK:  mov      dword ptr [ebp-4], eax
+; CHECK:  sub      esp, 128
+; CHECK:  mov      dword ptr [ebp-8], esp
+; CHECK:  mov      eax, dword ptr [ebp-8]
+; CHECK:  mov      dword ptr [ebp-12], eax
+; CHECK:  movzx    eax, byte ptr [ebp-4]
+; CHECK:  mov      dword ptr [ebp-16], eax
+; CHECK:  sub      esp, 16
+; CHECK:  mov      ecx, dword ptr [ebp+12]
+; CHECK:  mov      dword ptr [esp], ecx
+; CHECK:  mov      edx, dword ptr [ebp-12]
+; CHECK:  mov      dword ptr [esp+4], edx
+; CHECK:  mov      ebx, dword ptr [ebp-16]
+; CHECK:  mov      dword ptr [esp+8], ebx
+; CHECK:  call     memcpy_helper2