address review comments

lib/spack/external/archspec/json/cpu/microarchitectures.json

@@ -2706,7 +2706,7 @@
         ],
         "clang" : [
           {
-            "versions": "9.0:12.99",
+            "versions": "9.0:12.0",
             "flags" : "-march=armv8.4-a"
           },
           {

lib/spack/spack/environment/environment.py

@@ -468,6 +468,18 @@ def from_dict(base_path, d):
 
     @property
     def _current_root(self):
+        """
+        Return the directory in which the view is currently implemented.
+
+        If the view is using renameat2 for atomic updates, self.root is a directory and the root
+        of the underlying implementation is the same as self.root.
+
+        If the view us using symlinks for atomic updates, self.root is a link and we read the link
+        to find the root of the underlying implementation of the view.
+
+        If self.root does not exist or is a regular file, there is no current implementation of the
+        view on the filesystem.
+        """
         if not os.path.islink(self.root):
             if os.path.isdir(self.root):
                 return self.root

lib/spack/spack/util/atomic_update.py

@@ -19,7 +19,7 @@
     # python links against libc, so we can treat this as a libc handle
     # we could also use CDLL("libc.so.6") but this is (irrelevantly) more future proof
     libc = ctypes.CDLL(None)
-except BaseException:
+except OSError:
     pass
 
 renameat2 = getattr(libc, "renameat2", None)