Unify alloca, outgoing arg, and prolog construction

tests_lit/llvm2ice_tests/int-arg.ll

 ; This file checks that Subzero generates code in accordance with the
 ; calling convention for integers.
 
 ; RUN: %if --need=target_X8632 --command %p2i --filetype=obj --disassemble \
 ; RUN:   --target x8632 -i %s --args -O2 -allow-externally-defined-symbols \
 ; RUN:   | %if --need=target_X8632 --command FileCheck %s
 
 ; TODO(jvoung): Stop skipping unimplemented parts (via --skip-unimplemented)
 ; once enough infrastructure is in. Also, switch to --filetype=obj
 ; when possible.
@@ skipping 259 matching lines @@
 
 declare void @killRegisters()
 
 define internal void @test_passing_integers(i32 %arg0, i32 %arg1, i32 %arg2, i32 %arg3, i32 %arg4, i32 %arg5, i32 %arg6) {
   call void @killRegisters()
   call void @IntArgs(i32 %arg6, i32 %arg5, i32 %arg4, i32 %arg3, i32 %arg2, i32 %arg1)
   ret void
 }
 
 ; CHECK-LABEL: test_passing_integers
-; CHECK-DAG: mov [[REG1:e.*]],DWORD PTR [esp+0x24]
-; CHECK-DAG: mov [[REG2:e.*]],DWORD PTR [esp+0x28]
-; CHECK-DAG: mov [[REG3:e.*]],DWORD PTR [esp+0x2c]
-; CHECK-DAG: mov [[REG4:e.*]],DWORD PTR [esp+0x30]
+; CHECK-DAG: mov [[REG1:e.*]],DWORD PTR [esp+0x44]
+; CHECK-DAG: mov [[REG2:e.*]],DWORD PTR [esp+0x48]
+; CHECK-DAG: mov [[REG3:e.*]],DWORD PTR [esp+0x4c]
+; CHECK-DAG: mov [[REG4:e.*]],DWORD PTR [esp+0x50]
 ; CHECK: mov DWORD PTR [esp]
 ; CHECK: mov DWORD PTR [esp+0x4]
 ; CHECK-DAG: mov DWORD PTR [esp+0x8],[[REG4]]
 ; CHECK-DAG: mov DWORD PTR [esp+0xc],[[REG3]]
 ; CHECK-DAG: mov DWORD PTR [esp+0x10],[[REG2]]
 ; CHECK-DAG: mov DWORD PTR [esp+0x14],[[REG1]]
 ; CHECK: call
 
 ; ARM32-LABEL: test_passing_integers
 ; ARM32-DAG: mov [[REG1:.*]], r1
 ; ARM32-DAG: mov [[REG2:.*]], r2
 ; ARM32-DAG: mov [[REG3:.*]], r3
 ; ARM32: str [[REG2]], [sp]
 ; ARM32: str [[REG1]], [sp, #4]
 ; ARM32-DAG: mov r0
 ; ARM32-DAG: mov r1
 ; ARM32-DAG: mov r2
 ; ARM32-DAG: mov r3, [[REG3]]
 ; ARM32: bl