qt: make partially buildable on macos (#38990)

- drop use_xcode = True, as this would lead to an attempt install Xcode (#34064)
- don't automatically build Qt Location with +opengl, as this is
  still broken

This built sucessfully with qt@5.15.10+opengl+dbus+phonon on ventura/arm without
Xcode installed (only command line tools) - I did not check with Xcode installed.

var/spack/repos/builtin/packages/qt/package.py

@@ -61,6 +61,7 @@ class Qt(Package):
     variant("gtk", default=False, description="Build with gtkplus.")
     variant("gui", default=True, description="Build the Qt GUI module and dependencies")
     variant("opengl", default=False, description="Build with OpenGL support.")
+    variant("location", default=False, when="+opengl", description="Build the Qt Location module.")
     variant("phonon", default=False, description="Build with phonon support.")
     variant("shared", default=True, description="Build shared libraries.")
     variant("sql", default=True, description="Build with SQL support.")
@@ -253,8 +254,6 @@ class Qt(Package):
             msg="Apple Silicon requires a very new version of qt",
         )
 
-    use_xcode = True
-
     # Mapping for compilers/systems in the QT 'mkspecs'
     compiler_mapping = {
         "intel": ("icc",),
@@ -712,6 +711,10 @@ def configure(self, spec, prefix):
             # https://wiki.qt.io/QtWayland
             config_args.extend(["-skip", "wayland"])
 
+        if "~location" in spec:
+            if version >= Version("5.15"):
+                config_args.extend(["-skip", "qtlocation"])
+
         if "~opengl" in spec:
             config_args.extend(["-skip", "multimedia"])
             config_args.extend(["-skip", "qt3d"])
@@ -722,9 +725,6 @@ def configure(self, spec, prefix):
             if version >= Version("5.14"):
                 config_args.extend(["-skip", "qtquick3d"])
 
-            if version >= Version("5.15"):
-                config_args.extend(["-skip", "qtlocation"])
-
         else:
             # v5.0: qt3d uses internal-only libassimp
             # v5.5: external-only libassimp