Allow filtering constraints with markers

Author: uranusjr

news/8724.bugfix

@@ -0,0 +1,2 @@
+2020 Resolver: Correctly handle marker evaluation in constraints and exclude
+them if their markers do not match the current environment.

src/pip/_internal/resolution/resolvelib/resolver.py

@@ -80,7 +80,8 @@ def resolve(self, root_reqs, check_supported_wheels):
                 problem = check_invalid_constraint_type(req)
                 if problem:
                     raise InstallationError(problem)
-
+                if not req.match_markers():
+                    continue
                 name = canonicalize_name(req.name)
                 if name in constraints:
                     constraints[name] = constraints[name] & req.specifier