Making some major changes

[DuilioPerez]

These are some major changes done:

1. Updated CMakeLists.txt to make it easy to maintain and to use. It adds the ability to compiile theibrary with the selected backends. At the same time, makes cimgui being findable by another CMake based project and install the shared and static version of the library in their corresponding location.
2. Updated the CMakeLists.txt in the test directory to link agains the shared library.
3. Updated cimgui.h, cimgui.cpp, cimgui_impl.h and cimgui_impl.cpp to include almost all backends.
   These are some remarks.
4. DirectX 12 and WebGPU was not include due a generation error. However, it is available in the root directory CMake file.
5. To add a new or modify any existing backend, just add an conditional or modify the include/link flags
6. You can specify as variables the full and compatibility version of the library. This makes easy to update the version.

[DuilioPerez]

With some minor, this modifications can work with DearImGui, not only cimgui

[sonoro1234]

If you run generate, most of your work will be lost!!!

[DuilioPerez]

I don't understand what do you mean. If is related to cmake, then there isn't any modification to source code. I've tested from Android and there aren't errors:

~/cimgui $ cmake -S . -B build -DCIMGUI_BACKEND_SDL3=ON -DCIMGUI_BACKEND_SDLRENDERER3=ON -DCMAKE_INSTALL_PREFIX=$PREFIX
-- The C compiler identification is Clang 20.1.3
-- The CXX compiler identification is Clang 20.1.3
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /data/data/com.termux/files/usr/bin/cc - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /data/data/com.termux/files/usr/bin/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Configuring done (4.6s)
-- Generating done (0.1s)
-- Build files have been written to: /data/data/com.termux/files/home/cimgui/build
~/cimgui $ cd build/
~/cimgui/build $ make install
[  5%] Building CXX object CMakeFiles/cimgui-Shared.dir/cimgui.cpp.o
[ 10%] Building CXX object CMakeFiles/cimgui-Shared.dir/cimgui_impl.cpp.o
[ 15%] Building CXX object CMakeFiles/cimgui-Shared.dir/imgui/imgui.cpp.o
[ 20%] Building CXX object CMakeFiles/cimgui-Shared.dir/imgui/imgui_demo.cpp.o
[ 25%] Building CXX object CMakeFiles/cimgui-Shared.dir/imgui/imgui_draw.cpp.o
[ 30%] Building CXX object CMakeFiles/cimgui-Shared.dir/imgui/imgui_tables.cpp.o
[ 35%] Building CXX object CMakeFiles/cimgui-Shared.dir/imgui/imgui_widgets.cpp.o
[ 40%] Building CXX object CMakeFiles/cimgui-Shared.dir/imgui/backends/imgui_impl_sdl3.cpp.o
[ 45%] Building CXX object CMakeFiles/cimgui-Shared.dir/imgui/backends/imgui_impl_sdlrenderer3.cpp.o
[ 50%] Linking CXX shared library libcimgui.so
[ 50%] Built target cimgui-Shared                                                                             [ 55%] Building CXX object CMakeFiles/cimgui-Static.dir/cimgui.cpp.o
[ 60%] Building CXX object CMakeFiles/cimgui-Static.dir/cimgui_impl.cpp.o                                     [ 65%] Building CXX object CMakeFiles/cimgui-Static.dir/imgui/imgui.cpp.o                                     [ 70%] Building CXX object CMakeFiles/cimgui-Static.dir/imgui/imgui_demo.cpp.o                                [ 75%] Building CXX object CMakeFiles/cimgui-Static.dir/imgui/imgui_draw.cpp.o
[ 80%] Building CXX object CMakeFiles/cimgui-Static.dir/imgui/imgui_tables.cpp.o                              [ 85%] Building CXX object CMakeFiles/cimgui-Static.dir/imgui/imgui_widgets.cpp.o                             [ 90%] Building CXX object CMakeFiles/cimgui-Static.dir/imgui/backends/imgui_impl_sdl3.cpp.o                  [ 95%] Building CXX object CMakeFiles/cimgui-Static.dir/imgui/backends/imgui_impl_sdlrenderer3.cpp.o
[100%] Linking CXX static library libcimgui.a
[100%] Built target cimgui-Static
Install the project...
-- Install configuration: "RelWithDebInfo"
-- Installing: /data/data/com.termux/files/usr/lib/libcimgui.so.1.91.9
-- Up-to-date: /data/data/com.termux/files/usr/lib/libcimgui.so.1
-- Up-to-date: /data/data/com.termux/files/usr/lib/libcimgui.so
-- Installing: /data/data/com.termux/files/usr/include/cimgui.h
-- Installing: /data/data/com.termux/files/usr/include/cimgui_impl.h
-- Installing: /data/data/com.termux/files/usr/lib/libcimgui.a
-- Old export file "/data/data/com.termux/files/usr/share/cimguiConfig/cmake/cimguiConfig.cmake" will be replaced.  Removing files [/data/data/com.termux/files/usr/share/cimguiConfig/cmake/cimguiConfig-relwithdebinfo.cmake].
-- Installing: /data/data/com.termux/files/usr/share/cimguiConfig/cmake/cimguiConfig.cmake
-- Installing: /data/data/com.termux/files/usr/share/cimguiConfig/cmake/cimguiConfig-relwithdebinfo.cmake
~/cimgui/build $

If is about generation of the header cimgui.h and cimgui_impl.h, then they was generated once, and the cmake doesn't generate again.

If you mean about GitHub Actions, then the workflow needs a small modification to generate all the backends in the cimgui.h and cimgui_impl.h. As far as I've tested, it can generate all of the except WebGPU and DirectX12

[sonoro1234]

If is about generation of the header cimgui.h and cimgui_impl.h, then they was generated once,

Every time imgui is updated generate must be run again

[DuilioPerez]

Now I've added some other changes like a pkg-config file and the option to target for Emscripten. If GitHub Actions rewrite some of my work with the cimgui.h, cimgui.c, cimgui_impl.h and cimgui_impl.c there is no problem. I've made a small change to GitHub workflow that will autogenerate the code for almost all the backends. The only backends that were not added was wgpu and dx12 that halt in the generation with error