mobile/bind/objc: treat warnings as errors in SeqTest.m

Warnings used to be invisible when running SeqTest.m through
go test. Treat warnings as errors and fix a bug that surfaced.

Change-Id: I81e7291635824cdb4a898c91db740f7aa10f3611
Reviewed-on: https://go-review.googlesource.com/21133
Reviewed-by: David Crawshaw <crawshaw@golang.org>

bind/objc/SeqTest.m

@@ -369,7 +369,7 @@ static int numI = 0;
 
 - (void)testIDup {
 	Number *want = [[Number alloc] init];
-	Number *got = GoTestpkgIDup(want);
+	Number *got = (Number *)GoTestpkgI2Dup(want);
 	XCTAssertEqual(got, want, @"ObjC object passed through Go should not be wrapped");
 }
 

bind/objc/xcodetest/xcodetest.xcodeproj/project.pbxproj

@@ -189,6 +189,7 @@
 					"DEBUG=1",
 					"$(inherited)",
 				);
+				GCC_TREAT_WARNINGS_AS_ERRORS = YES;
 				GCC_WARN_64_TO_32_BIT_CONVERSION = YES;
 				GCC_WARN_ABOUT_RETURN_TYPE = YES_ERROR;
 				GCC_WARN_UNDECLARED_SELECTOR = YES;
@@ -227,6 +228,7 @@
 				ENABLE_STRICT_OBJC_MSGSEND = YES;
 				GCC_C_LANGUAGE_STANDARD = gnu99;
 				GCC_NO_COMMON_BLOCKS = YES;
+				GCC_TREAT_WARNINGS_AS_ERRORS = YES;
 				GCC_WARN_64_TO_32_BIT_CONVERSION = YES;
 				GCC_WARN_ABOUT_RETURN_TYPE = YES_ERROR;
 				GCC_WARN_UNDECLARED_SELECTOR = YES;

bind/testpkg/testpkg.go

@@ -143,6 +143,10 @@ func NumSCollected() int {
 	return numSCollected
 }
 
+func I2Dup(i I2) I2 {
+	return i
+}
+
 func IDup(i I) I {
 	return i
 }