Reduce number of external symbols in libllvm, libclang and liblldbHEADmain

In commit 2e47f35be5dc libllvm, libclang and liblldb were converted into
private shared libraries. This allowed clang, lld, lldb, and other llvm
tools to be linked against these shared libraries, which makes them
smaller and avoids duplication.

However, upstream builds the shared libraries using several visibility
options, which reduces the number of external symbols, and makes the
libraries a bit smaller.

On my test machine:
* libprivatellvm.so goes from 75643 to 34706 symbols (~54% reduction)
* libprivateclang.so goes from 53250 to 33531 symbols (~37% reduction)
* libprivatelldb.so goes from 27242 to 18798 symbols (~31% reduction)

Note: to get the full benefit, a clean build is required. Incremental
builds should still work, but I didn't want to force a full rebuild on
everybody.

MFC after:	1 week

0 files changed, 0 insertions, 0 deletions