Squash merge aosp/dev doc changes to aosp/master

711590 - Disable build.py in external/clang
711593 - Remove stray 'f'.
712465 - Further clarify build.py deprecation

Test: N/A
Change-Id: I42dacdfb4c974cd1cc2f5064154dec88683d3095
diff --git a/build.py b/build.py
index c16eee9..1411a7e 100755
--- a/build.py
+++ b/build.py
@@ -742,4 +742,7 @@
 
 
 if __name__ == '__main__':
-    main()
+    print 'This script and llvm branch are deprecated and unmaintained.'
+    print 'Use the llvm-toolchain branch (repo init ... -b llvm-toolchain).'
+    print 'https://android.googlesource.com/toolchain/llvm_android/+/master'
+    sys.exit(0)