x86: Fix calling convention for ffi_closure_win64_inner

Also enable testing for the cross-abi calls.

testsuite/lib/libffi.exp

@@ -315,6 +315,11 @@ proc run-many-tests { testcases extra_flags } {
                 "-DABI_NUM=FFI_THISCALL -DABI_ATTR=__THISCALL__"
                 "-DABI_NUM=FFI_FASTCALL -DABI_ATTR=__FASTCALL__"
             }
+        } elseif [istarget "x86_64-*-*"] {
+            set targetabis {
+                ""
+                "-DABI_NUM=FFI_WIN64 -DABI_ATTR=__MSABI__"
+            }
         }
     }
 

testsuite/libffi.call/ffitest.h

@@ -24,6 +24,7 @@
 #define __STDCALL__ __attribute__((stdcall))
 #define __THISCALL__ __attribute__((thiscall))
 #define __FASTCALL__ __attribute__((fastcall))
+#define __MSABI__ __attribute__((ms_abi))
 #else
 #define __UNUSED__
 #define __STDCALL__ __stdcall