Retrieve environment-modules prefix based on architecture (#10975)

When multiple instances of environment-modules were installed with
different architectures, Spack was not retrieving the installation
appropriate for the current architecture when finding the module
prefix.

lib/spack/spack/main.py

@@ -584,7 +584,8 @@ def shell_set(var, value):
     # print environment module system if available. This can be expensive
     # on clusters, so skip it if not needed.
     if 'modules' in info:
-        specs = spack.store.db.query('environment-modules')
+        specs = spack.store.db.query(
+            'environment-modules arch=%s' % spack.architecture.sys_type())
         if specs:
             shell_set('_sp_module_prefix', specs[-1].prefix)
         else: