title: CMake: target_include_directories() can't find header files
body: <p>At the top of my <code>main.cpp</code> file, <code>No such file or directory</code> is thrown at <code>#include &lt;sqlite3.h&gt;</code>.</p>
  
  <p>Building the code manually by <code>g++ -I"C:\Libraries\64_bit\SQLite3\include\" -L"C:\Libraries\64_bit\SQLite3\bin\" -lsqlite3 main.cpp Class1.cpp Class1.h Class2.cpp Class2.h -o main</code> throws no errors.</p>
  
  <p>CMake cannot seem to find the header, even though I've explicitly described where it is located in my file-system. According to the documentation for <a href="https://cmake.org/cmake/help/v3.7/command/target_include_directories.html" rel="nofollow noreferrer"><code>target_include_directories()</code></a>, that should be enough:</p>
  
  <blockquote>
    <p>Specified include directories may be absolute paths or relative paths. Repeated calls for the same  append items in the order called.</p>
  </blockquote>
  
  <p><strong>Why is the <code>target_include_directories()</code> function not finding the headers, even though I've provided the exact absolute path?</strong></p>
  
  <p>I'm developing on a 64-bit Windows 10 machine, and CLion is set-up to compile with the MinGW-w64 <code>g++</code> compiler.</p>
  
  <ul>
  <li>I've downloaded the 64-bit Windows pre-compiled binary, <code>sqlite3.dll</code> and stored it locally in <code>C:\Libraries\64_bit\SQLite3\bin\</code>. </li>
  <li>In order to access SQLite C++ functions I've also downloaded SQLite3's amalgamated source code and stored all source files in <code>C:\Libraries\64_bit\SQLite3\include\</code>.</li>
  </ul>
  
  <p>I built my project in CLion, which is essentially a fancy GUI-wrapper for CMake. In my <code>CMakeLists.txt</code>, I've included SQLite3's headers and linked <code>sqlite3</code> as follows:</p>
  
  <pre><code>cmake_minimum_required(VERSION 3.7)
  project(My_Project)
  
  set(CMAKE_CXX_STANDARD 11)
  
  set(INCLUDE_DIRS C:\\Libraries\\64_bit\\SQLite3\\include\\)
  set(LIBRARIES sqlite3.dll)
  # My project's source code
  set(SOURCE_FILES main.cpp Class1.cpp Class1.h Class2.cpp Class2.h)
  
  add_executable(My_Project ${SOURCE_FILES})
  
  # For compiler warnings
  target_compile_options(My_Project PRIVATE -Wall)
  # Including SQLite3's headers
  target_include_directories(My_Project PRIVATE ${INCLUDE_DIRS})
  # Linking against sqlite3.dll
  target_link_libraries(My_Project ${LIBRARIES})
  </code></pre>