buildsystem: adjust build system priorities

Lower is better, and we want autotools to always be the preferred build
system until we have either 1) rearchitected multi-build systems or 2)
decided on another "blessed" build system.

plugins/cargo/cargo_plugin.py

@@ -62,8 +62,7 @@ class CargoBuildSystem(Ide.Object, Ide.BuildSystem, Gio.AsyncInitable):
         return task.propagate_boolean()
 
     def do_get_priority(self):
-        # Priority is used to determine the order of discovery
-        return 2000
+        return 300
 
 class CargoPipelineAddin(Ide.Object, Ide.BuildPipelineAddin):
     """

plugins/cmake/cmake_plugin/__init__.py

@@ -50,7 +50,7 @@ class CMakeBuildSystem(Ide.Object, Ide.BuildSystem, Gio.AsyncInitable):
         return result.propagate_boolean()
 
     def do_get_priority(self):
-        return -300 # Lower priority than Autotools for now
+        return 200
 
 
 class CMakePipelineAddin(Ide.Object, Ide.BuildPipelineAddin):

plugins/meson/meson_plugin/__init__.py

@@ -78,7 +78,7 @@ class MesonBuildSystem(Ide.Object, Ide.BuildSystem, Gio.AsyncInitable):
         return result.propagate_boolean()
 
     def do_get_priority(self):
-        return -200 # Lower priority than Autotools for now
+        return 100
 
     def do_get_build_flags_async(self, ifile, cancellable, callback, data=None):
         task = Gio.Task.new(self, cancellable, callback)