misc/cgo/testcdefs: comment out test of packed structs

The [568]c compilers no longer support packed structs, so
using them with -cdefs no longer works.  Just commenting out
the test, rather than removing it, in case this needs to be
handled.  It may be that -cdefs can go away entirely in the
future, in which case so can this directory.

LGTM=mdempsky
R=rsc, mdempsky
CC=golang-codereviews
https://golang.org/cl/136030043

misc/cgo/testcdefs/cdefstest.go

@@ -56,4 +56,5 @@ typedef struct timespec {
 import "C"
 
 type CdefsTest C.struct_cdefsTest
-type PackedTest C.struct_packedTest
+
+//type PackedTest C.struct_packedTest

misc/cgo/testcdefs/main.c

@@ -17,6 +17,8 @@ struct CdefsOrig {
 	int8 **array5[20][20];
 };
 
+// Packed structs are no longer supported for -cdefs.
+/*
 typedef struct PackedOrig PackedOrig;
 #pragma pack on
 struct PackedOrig {
@@ -25,14 +27,15 @@ struct PackedOrig {
 	int64 third;
 };
 #pragma pack off
+*/
 
 void
 main·test(int32 ret)
 {
 	CdefsOrig o;
 	CdefsTest t;
-	PackedOrig po;
-	PackedTest pt;
+	// PackedOrig po;
+	// PackedTest pt;
 	
 	ret = 0;
 	if(sizeof(t.array1) != sizeof(o.array1) || offsetof(CdefsTest, array1[0]) != offsetof(CdefsOrig, array1[0])) {
@@ -55,6 +58,7 @@ main·test(int32 ret)
 		runtime·printf("array5: size, offset = %d, %d, want %d, %d\n", sizeof(t.array5), offsetof(CdefsTest, array5[0][0]), sizeof(o.array5), offsetof(CdefsOrig, array5[0][0]));
 		ret = 1;
 	}
+/*
 	if(sizeof(pt.first) != sizeof(po.first) || offsetof(PackedTest, first) != offsetof(PackedOrig, first)) {
 		runtime·printf("first: size, offset = %d, %d, want %d, %d\n", sizeof(pt.first), offsetof(PackedTest, first), sizeof(po.first), offsetof(PackedOrig, first));
 		ret = 1;
@@ -67,5 +71,6 @@ main·test(int32 ret)
 		runtime·printf("third: size, offset = %d, %d, want %d, %d\n", sizeof(pt.third), offsetof(PackedTest, third), sizeof(po.third), offsetof(PackedOrig, third));
 		ret = 1;
 	}
+*/
 	FLUSH(&ret); // flush return value
 }