debuginstall: gracefully handle missing __file__ attributes

This was crashing PyOxidizer.  While here, point "Python lib" and "installed
modules" to the oxidized binary when read from memory instead of pretending
their location is unknown.

Differential Revision: https://phab.mercurial-scm.org/D7451

mercurial/debugcommands.py

@@ -1470,6 +1470,12 b' def debuginstall(ui, **opts):'
     )
 
     # Python
+    pythonlib = None
+    if util.safehasattr(os, '__file__'):
+        pythonlib = os.path.dirname(pycompat.fsencode(os.__file__))
+    elif getattr(sys, 'oxidized', False):
+        pythonlib = pycompat.sysexecutable
+
     fm.write(
         b'pythonexe',
         _(b"checking Python executable (%s)\n"),
@@ -1483,7 +1489,7 b' def debuginstall(ui, **opts):'
     fm.write(
         b'pythonlib',
         _(b"checking Python lib (%s)...\n"),
-        os.path.dirname(pycompat.fsencode(os.__file__)),
+        pythonlib or _(b"unknown"),
     )
 
     security = set(sslutil.supportedprotocols)
@@ -1527,13 +1533,19 b' def debuginstall(ui, **opts):'
     )
 
     # compiled modules
+    hgmodules = None
+    if util.safehasattr(sys.modules[__name__], '__file__'):
+        hgmodules = os.path.dirname(pycompat.fsencode(__file__))
+    elif getattr(sys, 'oxidized', False):
+        hgmodules = pycompat.sysexecutable
+
     fm.write(
         b'hgmodulepolicy', _(b"checking module policy (%s)\n"), policy.policy
     )
     fm.write(
         b'hgmodules',
         _(b"checking installed modules (%s)...\n"),
-        os.path.dirname(pycompat.fsencode(__file__)),
+        hgmodules or _(b"unknown"),
     )
 
     rustandc = policy.policy in (b'rust+c', b'rust+c-allow')