Documentation: Add documentation how to build Qt Creator with CMake

Change-Id: I36617ce09301165f2e18a7524a18283264957ac6
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@qt.io>

README.md

@@ -31,6 +31,7 @@ Prerequisites:
     * ActiveState Active Perl
     * MinGW with g++ 5.3 or Visual Studio 2017 or later
     * jom
+    * Ninja (optional, needed for CMake)
     * Python 3.5 or later (optional, needed for the python enabled debug helper)
 * On Mac OS X: latest Xcode
 * On Linux: g++ 5.3 or later
@@ -38,7 +39,7 @@ Prerequisites:
   Clang PCH Manager and Clang Refactoring plugins, see the section
   "Get LLVM/Clang for the Clang Code Model". The LLVM C++ API provides no compatibility garantee,
   so if later versions don't compile we don't support that version.)
-* CMake (only for manual builds of LLVM/Clang)
+* CMake (for manual builds of LLVM/Clang, and Qt Creator itself)
 * Qbs 1.7.x (optional, sources also contain Qbs itself)
 
 The installed toolchains have to match the one Qt was compiled with.
@@ -264,13 +265,24 @@ http://llvm.org/docs/GettingStarted.html#git-mirror:
 
       For Linux/macOS:
 
-          cmake -DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_RTTI=ON -DLLVM_ENABLE_PROJECTS="clang;clang-tools-extra" -DCMAKE_INSTALL_PREFIX=<installation location> ../llvm-project/llvm
-          make install
+          cmake \
+            -D CMAKE_BUILD_TYPE=Release \
+            -D LLVM_ENABLE_RTTI=ON \
+            -D LLVM_ENABLE_PROJECTS="clang;clang-tools-extra" \
+            -D CMAKE_INSTALL_PREFIX=<installation location> \
+            ../llvm-project/llvm
+          cmake --build . --target install
 
       For Windows:
 
-          cmake -G "NMake Makefiles JOM" -DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_RTTI=ON -DLLVM_ENABLE_PROJECTS="clang;clang-tools-extra" -DCMAKE_INSTALL_PREFIX=<installation location> ..\llvm-project\llvm
-          jom install
+          cmake ^
+            -G "NMake Makefiles JOM" ^
+            -D CMAKE_BUILD_TYPE=Release ^
+            -D LLVM_ENABLE_RTTI=ON ^
+            -D LLVM_ENABLE_PROJECTS="clang;clang-tools-extra" ^
+            -D CMAKE_INSTALL_PREFIX=<installation location> ^
+            ..\llvm-project\llvm
+          cmake --build . --target install
 
 ### Clang-Format
 
@@ -282,6 +294,34 @@ While the plugin builds without it, it will be disabled on start with an error m
 
 Note that the plugin is disabled by default.
 
+### Building Qt Creator with CMake
+
+Qt Creator can also be built with CMake. The main Qt Creator dependencies, Qt and LLVM/Clang, both
+offer CMake find packages, which reduce the steps of configuring Qt Creator to a minimum.
+
+   Configure and build Qt Creator:
+
+      mkdir build
+      cd build
+
+    For Linux/macOS:
+
+      cmake \
+        -G Ninja \
+        -D CMAKE_BUILD_TYPE=Release \
+        -D CMAKE_PREFIX_PATH=~/Qt/5.12.5/gcc_64;~/llvm \
+        ../qt-creator
+      cmake --build .
+
+    For Windows:
+
+      cmake ^
+        -G Ninja ^
+        -D CMAKE_BUILD_TYPE=Release ^
+        -D CMAKE_PREFIX_PATH=c:\Qt\5.12.5\msvc2017_64;c:\llvm ^
+        ..\qt-creator
+      cmake --build .
+
 ## Third-party Components
 
 Qt Creator includes the following third-party components,