Bug#848368: llvm-toolchain-3.9: Please add ELF symbols versions to the libraries

[Rebecca N. Palmer]

Thanks, but I think we missed something: as packages rebuilt against new 
(versioned-symbols) LLVM don't work with old LLVM, we need a shlibs bump 
to make dependencies reflect that (i.e. require upgrading 
libllvm/libclang before their dependencies).  I think that's

--- /dev/null
+++ a/debian/liblldb-3.9.shlibs
@@ -0,0 +1 @@
+liblldb-3.9 1 liblldb-3.9 (>= 1:3.9.1-6~)
--- /dev/null
+++ a/debian/libllvm3.9.shlibs
@@ -0,0 +1 @@
+libLLVM-3.9 1 libllvm3.9 (>= 1:3.9.1-6~)

and either change every symbol's minimum version in 
libclang1-X.Y.symbols.in to 1:3.9.1-6~, or delete the symbols file (why 
does a library this API-unstable even have one?) and create a shlibs 
file similar to the above.  However, I have not tested this.

dh_makeshlibs -V in debian/rules would also work, but would become 
unnecessarily restrictive if future versions retain it.

Also, #857623 (the OpenCL bug) also affects 3.8 and 4.0; the same fix 
should work.