Added additional option "sort" to supply a sorting script to specify
the order of files when compiled into a library;  this allows the
Makefile to enforce natural sort order and/or put dependent entries
at the top.  Also added a custom script for sky130 to handle the
assortment of "include" statements in the standard cell verilog
before generating the library files.
diff --git a/common/create_spice_library.py b/common/create_spice_library.py
index ca95fa6..90d4e65 100755
--- a/common/create_spice_library.py
+++ b/common/create_spice_library.py
@@ -55,16 +55,24 @@
     if os.path.isfile(outputname):
         os.remove(outputname)
 
-    if fformat == 'CDL':
-        slist = glob.glob(destlibdir + '/*.cdl')
+    # If file "filelist.txt" exists in the directory, get the list of files from it
+    if os.path.exists(destlibdir + '/filelist.txt'):
+        with open(destlibdir + '/filelist.txt', 'r') as ifile:
+            rlist = ifile.read().splitlines()
+            slist = []
+            for rfile in rlist:
+                slist.append(destlibdir + '/' + rfile)
     else:
-        # Sadly, there is no consensus on what a SPICE file extension should be.
-        slist = glob.glob(destlibdir + '/*.spc')
-        slist.extend(glob.glob(destlibdir + '/*.spice'))
-        slist.extend(glob.glob(destlibdir + '/*.spi'))
-        slist.extend(glob.glob(destlibdir + '/*.ckt'))
-        slist.extend(glob.glob(destlibdir + '/*.cir'))
-        slist.extend(glob.glob(destlibdir + '/*' + spiext))
+        if fformat == 'CDL':
+            slist = glob.glob(destlibdir + '/*.cdl')
+        else:
+            # Sadly, there is no consensus on what a SPICE file extension should be.
+            slist = glob.glob(destlibdir + '/*.spc')
+            slist.extend(glob.glob(destlibdir + '/*.spice'))
+            slist.extend(glob.glob(destlibdir + '/*.spi'))
+            slist.extend(glob.glob(destlibdir + '/*.ckt'))
+            slist.extend(glob.glob(destlibdir + '/*.cir'))
+            slist.extend(glob.glob(destlibdir + '/*' + spiext))
 
     if alllibname in slist:
         slist.remove(alllibname)