Migrate cmake docs to the godot docs.

(cherry picked from commit c7873e1)

Author: Ivorforce

CMakeLists.txt

@@ -21,7 +21,8 @@ compromises need to be made to resolve those differences.
 As we are attempting to maintain feature parity, and ease of maintenance, these
 CMake scripts are built to resemble the SCons build system wherever possible.
 Where they are not, we will attempt to document common difference in
-doc/cmake.rst and platform specific differences in their respective
+the docs (https://docs.godotengine.org/en/latest/tutorials/scripting/cpp/build_system/cmake.html)
+and platform specific differences in their respective
 cmake/<platform>.cmake file.
 
 The file structure and file content are made to match, if not in content then

cmake/android.cmake

@@ -22,16 +22,16 @@ Android platforms.
 
 .. _built-in support:https://cmake.org/cmake/help/latest/manual/cmake-toolchains.7.html#cross-compiling-for-android
 
-There is further information and examples in the doc/cmake.rst file.
+There is further information and examples in the docs: https://docs.godotengine.org/en/latest/tutorials/scripting/cpp/build_system/cmake.html
 
 ]=======================================================================]
 
 #[============================[ Android Options ]============================]
 function(android_options)
     #[[ Options from SCons
 
-    The options below are managed by CMake toolchain files, doc.cmake.rst has
-    more information
+    The options below are managed by CMake toolchain files, the docs have more information:
+    https://docs.godotengine.org/en/latest/tutorials/scripting/cpp/build_system/cmake.html
 
     android_api_level : Target Android API level.
         Default = 21

cmake/linux.cmake

@@ -12,7 +12,8 @@ function(linux_options)
     #[[ Options from SCons
     use_llvm : Use the LLVM compiler
         Not implemented as compiler selection is managed by CMake. Look to
-        doc/cmake.rst for examples.
+        the docs (https://docs.godotengine.org/en/latest/tutorials/scripting/cpp/build_system/cmake.html)
+        for examples.
     ]]
     option(GODOTCPP_USE_STATIC_CPP "Link libgcc and libstdc++ statically for better portability" ON)
 endfunction()

cmake/windows.cmake

@@ -62,7 +62,9 @@ function(windows_options)
         Default: True
 
     These three options will not implemented as compiler selection is managed
-    by CMake toolchain files. Look to doc/cmake.rst for examples.
+    by CMake toolchain files. Look to the docs
+    (https://docs.godotengine.org/en/latest/tutorials/scripting/cpp/build_system/cmake.html)
+    for examples.
     use_mingw: Use the MinGW compiler instead of MSVC - only effective on Windows
     use_llvm: Use the LLVM compiler (MVSC or MinGW depending on the use_mingw flag
     mingw_prefix: MinGW prefix