libffi fix

Closes PR 13707

src/foreign/README

@@ -20,6 +20,9 @@ Local changes:
  * In "x86/darwin.S", added ".long 0" after ".LFE3:" to avoid
    linker problems compiling with gcc-4.0 on Mac OS X 10.7.
 
+ * In "x86/ffi.c" for Win32, don't try to align stack for
+   stdcall, fastcall, or thiscall.
+
 ========== libffi_msvc directory =====================================
 
 This directory is synced from the CTypes repository

src/foreign/libffi/src/x86/ffi.c

@@ -315,7 +315,12 @@ ffi_status ffi_prep_cif_machdep(ffi_cif *cif)
   cif->bytes += 4 * sizeof(ffi_arg);
 #endif
 
-  cif->bytes = (cif->bytes + 15) & ~0xF;
+#ifdef X86_WIN32
+  if ((cif->abi != FFI_STDCALL)
+      && (cif->abi != FFI_FASTCALL)
+      && (cif->abi != FFI_THISCALL))
+#endif
+    cif->bytes = (cif->bytes + 15) & ~0xF;
 
   return FFI_OK;
 }