misc/cgo/test: fix go vet warnings

Fixes these warnings from go vet:
buildid_linux.go:25: no formatting directive in Fatalf call
callback.go:180: arg pc[i] for printf verb %p of wrong type: uintptr
env.go:34: possible misuse of unsafe.Pointer
issue7665.go:22: possible misuse of unsafe.Pointer

Change-Id: I83811b9c10c617139713a626b4a34ab05564d4fe
Reviewed-on: https://go-review.googlesource.com/15802Reviewed-by: David Crawshaw <crawshaw@golang.org>

misc/cgo/test/buildid_linux.go

@@ -22,7 +22,7 @@ func testBuildID(t *testing.T) {
 		if os.IsNotExist(err) {
 			t.Skip("no /proc/self/exe")
 		}
-		t.Fatalf("opening /proc/self/exe: ", err)
+		t.Fatal("opening /proc/self/exe: ", err)
 	}
 	defer f.Close()
 

misc/cgo/test/callback.go

@@ -177,7 +177,7 @@ func testCallbackCallers(t *testing.T) {
 	for i := 0; i < n; i++ {
 		f := runtime.FuncForPC(pc[i])
 		if f == nil {
-			t.Fatalf("expected non-nil Func for pc %p", pc[i])
+			t.Fatalf("expected non-nil Func for pc %d", pc[i])
 		}
 		fname := f.Name()
 		// Remove the prepended pathname from automatically

misc/cgo/test/env.go

@@ -31,7 +31,7 @@ func testSetEnv(t *testing.T) {
 	keyc := C.CString(key)
 	defer C.free(unsafe.Pointer(keyc))
 	v := C.getenv(keyc)
-	if v == (*C.char)(unsafe.Pointer(uintptr(0))) {
+	if uintptr(unsafe.Pointer(v)) == 0 {
 		t.Fatal("getenv returned NULL")
 	}
 	vs := C.GoString(v)

misc/cgo/test/issue7665.go

@@ -19,7 +19,7 @@ var bad7665 unsafe.Pointer = C.f7665
 var good7665 uintptr = uintptr(C.f7665)
 
 func test7665(t *testing.T) {
-	if bad7665 == nil || bad7665 != unsafe.Pointer(good7665) {
+	if bad7665 == nil || uintptr(bad7665) != good7665 {
 		t.Errorf("ptrs = %p, %#x, want same non-nil pointer", bad7665, good7665)
 	}
 }