MS inline asm: Use memory constraints for functions instead of registers

This is consistent with how we parse them in a standalone .s file, and
inline assembly shouldn't differ.

This fixes errors about requiring more registers than available in
cases like this:
  void f();
  void __declspec(naked) g() {
    __asm pusha
    __asm call f
    __asm popa
    __asm ret
  }

There are no registers available to pass the address of 'f' into the asm
blob.  The asm should now directly call 'f'.

Tests will land in Clang shortly.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@214550 91177308-0d34-0410-b5e6-96231b3b80d8

test/CodeGen/X86/ms-inline-asm.ll

@@ -110,7 +110,7 @@ define i32 @t31() {
 entry:
   %val = alloca i32, align 64
   store i32 -1, i32* %val, align 64
-  call void asm sideeffect inteldialect "mov dword ptr $0, esp", "=*m,~{dirflag},~{fpsr},~{flags}"(i32* %val) #1
+  call void asm sideeffect inteldialect "mov dword ptr $0, esp", "=*m,~{dirflag},~{fpsr},~{flags}"(i32* %val)
   %sp = load i32* %val, align 64
   ret i32 %sp
 ; CHECK-LABEL: t31:
@@ -125,3 +125,12 @@ entry:
 ; CHECK: movl (%esp), %eax
 ; CHECK: ret
 }
+
+declare void @other_func()
+
+define void @naked() #0 {
+  call void asm sideeffect inteldialect "call dword ptr $0", "*m,~{eax},~{ebx},~{ecx},~{edx},~{edi},~{esi},~{esp},~{ebp},~{dirflag},~{fpsr},~{flags}"(void()* @other_func)
+  unreachable
+}
+
+attributes #0 = { naked }