Update to the latest upstream p7zip version

This version has a fix integrated upstream for the issue with
multiple files containing the same data in solid NSIS archives.

Author: mstorsjo

sdks/7z/7z

@@ -1,13 +1,13 @@
 
 The included binary is for linux/x86. If it doesn't work for you, you need
-to compile it from source, a patch that is not integrated upstream yet is
-needed.
+either remove it (and let the install script use 7z from somewhere else
+in your PATH; however, it must be at least version 9.20) or compile it
+from source.
 
 To compile it from source on OS X:
 
-tar -jxvf p7zip_9.13_src_all.tar.bz2
-cd p7zip_9.13
-patch -p1 < ../p7zip.patch
+tar -jxvf p7zip_9.20.1_src_all.tar.bz2
+cd p7zip_9.20.1
 cp makefile.macosx_64bits makefile.machine
 make 7z
 cp bin/7z ..