Add "interface hash" for improved incremental builds.

Compute the hash of all interface tokens when parsing; write the
interface hash to the swiftdeps file, or if the -dump-interface-hash
option is passed to the frontend. This hash will be used in incremental
mode to determine whether a file's interface has changed, and therefore
whether dependent files need to be rebuilt in response to the change.

Committed on ChrisW's behalf while he gets his setup unborked.

rdar://problem/15352929

Swift SVN r30477

utils/split_file.py

@@ -0,0 +1,49 @@
+#!/usr/bin/env python
+
+"""
+split_file.py [-o <dir>] <path>
+
+Take the file at <path> and write it to multiple files, switching to a new file
+every time an annotation of the form "// BEGIN file1.swift" is encountered. If
+<dir> is specified, place the files in <dir>; otherwise, put them in the
+current directory.
+"""
+
+import os
+import sys
+import re
+import getopt
+
+def usage():
+    sys.stderr.write(__doc__.strip() + "\n")
+    sys.exit(1)
+
+fp_out = None
+dest_dir = '.'
+
+try:
+    opts, args = getopt.getopt(sys.argv[1:], 'o:h')
+    for (opt, arg) in opts:
+        if opt == '-o':
+            dest_dir = arg
+        elif opt == '-h':
+            usage()
+except getopt.GetoptError:
+    usage()
+
+if len(args) != 1:
+    usage()
+fp_in = open(args[0], 'r')
+
+for line in fp_in:
+    m = re.match(r'^//\s*BEGIN\s+([^\s]+)\s*$', line)
+    if m:
+        if fp_out:
+            fp_out.close()
+        fp_out = open(os.path.join(dest_dir, m.group(1)), 'w')
+    elif fp_out:
+        fp_out.write(line)
+
+fp_in.close()
+if fp_out:
+    fp_out.close()