Avoid hardcoding the underlying build tool

Since 3.15, not only --build can call the low-level build tool,
--install can also be used to run the installation. There's also an
environment variable that can be used to control the backend at cmake
time, but that may only be useful later.

Change-Id: I8c1ee48f946e110af3e824cf8980bbacbb94db99
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@qt.io>
Reviewed-by: Qt CMake Build Bot

coin/module_config.yaml

@@ -171,11 +171,17 @@ build_instructions:
     maxTimeInSeconds: 60
     userMessageOnFailure: Could not print the file cmake config file. This should not be possible.
   - type: ExecuteCommand
-    command: "{{.Env.ENV_PREFIX}} ninja install"
+    command: "{{.Env.ENV_PREFIX}} cmake --build ."
     maxTimeInSeconds: 6000
     maxTimeBetweenOutput: 120
     userMessageOnFailure: >
       Failed to build sources. In the current state bug can be everywhere. Contact Liang first.
+  - type: ExecuteCommand
+    command: "{{.Env.ENV_PREFIX}} cmake --install ."
+    maxTimeInSeconds: 6000
+    maxTimeBetweenOutput: 120
+    userMessageOnFailure: >
+      Failed to install sources. In the current state bug can be everywhere. Contact Liang first.
   - type: SignPackage
     enable_if:
       condition: property