Bug#913946: llvm*7 unstripped

[Rebecca N. Palmer]

Control: retitle -1 llvm*-dbgsym not built "failed to find link section"
(the llvm-strip fix attempt has been reverted)

The original errors with GNU strip appear to be this upstream bug:

https://sourceware.org/bugzilla/show_bug.cgi?id=23788
https://bugs.llvm.org/show_bug.cgi?id=39359

This description suggests it is widespread in code built by Clang, and 
can be avoided by passing -fno-addrsig 
(http://clang.llvm.org/docs/UsersManual.html#cmdoption-faddrsig).

It has been fixed upstream in GNU strip, but the fixed version is not 
expected to be in Debian before freeze: 
https://lists.debian.org/debian-gcc/2018/07/msg00036.html