Restore compatibility with macOS 10.14 (Mudlet#4793)

* Set XCode to 11.3 which is what we used in Travis

* Set CMAKE_OSX_DEPLOYMENT_TARGET correctly

* Correct CMakeLists

* Fix syntax

* Up to latest available XCode

.github/workflows/build-mudlet.yml

@@ -139,6 +139,9 @@ jobs:
         echo "LUA_PATH=$LUA_PATH" >> $GITHUB_ENV
         echo "LUA_CPATH=$LUA_CPATH" >> $GITHUB_ENV
 
+        # Use latest available XCode
+        echo "DEVELOPER_DIR=/Applications/Xcode_12.4.app/Contents/Developer" >> $GITHUB_ENV
+
     - name: (Linux) Install non-vcpkg dependencies
       if: runner.os == 'Linux'
       run: |

CMakeLists.txt

@@ -36,10 +36,7 @@
 cmake_minimum_required(VERSION 3.3)
 
 if(APPLE)
-  set(CMAKE_OSX_DEPLOYMENT_TARGET "10.13") # Qt 5.11.2 with which we build on OS
-                                           # X supports 10.11 and up, but some
-                                           # tools are not provided as bottles
-                                           # for that anymore.
+  set(CMAKE_OSX_DEPLOYMENT_TARGET "10.14" CACHE STRING "")
 endif()
 
 project(mudlet)