Allow to build KDMqtt on macOS

* adapt FindMosquitto.cmake for macOS
* (re)enable macOS CI run

.github/workflows/build.yml

@@ -18,7 +18,7 @@ jobs:
           #- ubuntu-20.04 -> disabled during introduction of KDMqtt
           - windows-2022
           #- windows-2019
-          #- macos-12 -> disabled during introduction of KDMqtt
+          - macos-12
           #- macos-11
         build_type:
           - Debug
@@ -50,6 +50,12 @@ jobs:
           libwayland-dev xvfb ninja-build \
           libmosquittopp-dev
 
+      - name: Download mosquitto (MacOS)
+        if: runner.os == 'macOS'
+        run: |
+          brew update
+          brew install mosquitto
+
       - name: Download mosquitto (Windows)
         if: runner.os == 'Windows'
         run: |

cmake/FindMosquitto.cmake

@@ -14,17 +14,19 @@ find_file(MOSQUITTO_HEADER
     PATHS
         /usr/include
         /usr/local/include
+        /usr/local/opt/mosquitto/include
         $ENV{PROGRAMFILES}/mosquitto/devel
         $ENV{PROGRAMFILES\(X86\)}/mosquitto/devel
 )
 
-if(UNIX)
+if(APPLE OR UNIX)
     find_library(MOSQUITTO_LIBRARY
         NAMES
             mosquitto
         PATHS
             /usr/lib
             /usr/local/lib
+            /usr/local/opt/mosquitto/lib
     )
 
     if(MOSQUITTO_HEADER AND MOSQUITTO_LIBRARY)
@@ -64,7 +66,7 @@ if(Mosquitto_FOUND)
 
     add_library(Mosquitto::Mosquitto SHARED IMPORTED)
 
-    if(UNIX)
+    if(APPLE OR UNIX)
         set_target_properties(Mosquitto::Mosquitto PROPERTIES
             IMPORTED_LOCATION "${MOSQUITTO_LIBRARY}"
             INTERFACE_INCLUDE_DIRECTORIES "${MOSQUITTO_INCLUDE_DIRECTORY}"