What difference: -lX11 option vs. target_link_libraries in CMake - makefile

Question

I need to use OpenGL as a library in my project on my Ubuntu 15.04 64bit PC, which is built by CMake 3.0.2. I install packages: mesa-common-dev mesa-utils-extra libgl1-mesa-dev libglu1-mesa-dev libglapi-mesa libx11-dev libxi-dev libxinerama-dev libxcursor-dev libxrandr-dev
After run cmake and Makefile, I got these link error:
/usr/bin/ld: /home/user/CMU462/DrawSVG/asst1_drawsvg/lib/libglfw.a(x11_window.c.o): undefined reference to symbol 'XConvertSelection'
/usr/lib/gcc/x86_64-linux-gnu/4.9/../../../x86_64-linux-gnu/libX11.so: error adding symbols: DSO missing from command line
I checked /usr/lib/x86_64-linux-gnu/libX11.so, it does exist.
I found a explanation, it seems I failed to link my project with X11 library. The answer says that add -lX11 option may fix this.
Alternatively I link
X11 library in CMakeLists.txt according to FindX11.cmake:
find_package(X11 REQUIRED)
message(STATUS "X11_FOUND = ${X11_FOUND}")
message(STATUS "X11_INCLUDE_DIR = ${X11_INCLUDE_DIR}")
message(STATUS "X11_LIBRARIES = ${X11_LIBRARIES}")
include_directories(${X11_INCLUDE_DIR})
link_directories(${X11_LIBRARIES})
target_link_libraries(MyProj ... ${X11_LIBRARIES})
Run cmake I got these output:
-- X11_FOUND = 1
-- X11_INCLUDE_DIR = /usr/include
-- X11_LIBRARIES = /usr/lib/x86_64-linux-gnu/libX11.so;/usr/lib/x86_64-linux-gnu/libXext.so
But I still got the error aforementioned.
QUESTION: The X11 library can be linked by
using target_link_libraries in CMakeLists.txt, or
adding -lX11 option directly to compiling command
What's the difference between them? Does the link in CMakeLists.txt directly lead to a -lX11 option in Makefile generated?
If so, did I do something wrong in CMakeLists.txt?
UPDATE
Let's take this project as example, following is my build procedure.
Install required libraries: Install the OpenGL and other relative libraries (the GLEW and GLFW library is provided in this project): mesa-common-dev mesa-utils-extra libgl1-mesa-dev libglu1-mesa-dev libglapi-mesa libxi-dev libxinerama-dev libxcursor-dev libxrandr-dev
Run CMake: Then use the provided CMakeLists.txt, everything goes right.
Make: When make the project, this error occurred:
/usr/bin/ld: /home/user/CMU462/DrawSVG/asst1_drawsvg/lib/libglfw.a(x11_window.c.o): undefined reference to symbol 'XConvertSelection'
/usr/lib/gcc/x86_64-linux-gnu/4.9/../../../x86_64-linux-gnu/libX11.so: error adding symbols: DSO missing from command line
I have searched for many times, all of the answers say that the incorrect link of glfw3 and x11 lead to the error:
missing the -X11 option. However in line 26 of CMakeLists.txt exists this option
the libraries show arranged in order. I check the dependencies with pkg-config --libs command, all libraries are arranged in order in line 17 to 29 of CMakeLists.txt.
The only potential reason for this is the order of the compile options of libraries (line 17 to 29) and the target_link_libraries (line 116) of CMakeLists.txt.
Otherwise, there must be another error omitted by me during my procedure.