Corrected nearly all of the filter files, which will throw an
exception instead of a graceful error message if the input file
is not found.  The problem that exposed this error, though, was
a simple misplaced line in the sky130 Makefile, which has been
corrected.
diff --git a/sky130/custom/scripts/fixspice.py b/sky130/custom/scripts/fixspice.py
index a44cde8..73f6e3b 100755
--- a/sky130/custom/scripts/fixspice.py
+++ b/sky130/custom/scripts/fixspice.py
@@ -23,7 +23,7 @@
             # spilines = spitext.replace('\n+', ' ').splitlines()
             spilines = spitext.splitlines()
     except:
-        print('fixspice.py: failed to open ' + fnmIn + ' for reading.', file=sys.stderr)
+        print('fixspice.py: failed to open ' + inname + ' for reading.', file=sys.stderr)
         return 1
 
     # Process input with regexp