$ cat CMakeLists.txt
cmake_minimum_required(VERSION 3.0.2)
project(Issue15608 CXX)

find_package(Qt4)

set(CMAKE_INCLUDE_CURRENT_DIR ON)
set(CMAKE_AUTOMOC ON)
set(CMAKE_AUTORCC ON)

add_executable(bugtest
  main.cpp
  mainx.qrc
  )
target_link_libraries(bugtest Qt4::QtCore)

$ cat main.h
#include <QObject>

class tst1 : public QObject
{
  Q_OBJECT

 public slots:
   void onTst1();
   void onTst2();
};

$ cat main.cpp
#include "main.h"

void tst1::onTst1()
{
}

void tst1::onTst2()
{
}

int main( int argc, char **argv)
{
  return 0;
}

$ cat mainx.qrc
<!DOCTYPE RCC><RCC version="1.0">
<qresource>
  <file>foo.png</file>
</qresource>
</RCC>

$ test -f foo.png && echo exists
exists

$ cmake --version
cmake version 3.3.0-rc2

$ mkdir build
$ cd build

$ cmake .. -G "Visual Studio 10 2010" -DQT_QMAKE_EXECUTABLE=c:/.../bin/qmake
$ cmake --build . --config Debug
...
Build succeeded.
    0 Warning(s)
    0 Error(s)

$ cmake --build . --config Debug
...\build\moc_main.cpp(50): error C2039: 'onTst2' : is not a member of 'tst1'