s390x __tls_get_addr_internal vs. __tls_get_offset

Summary:
Symbol __tls_get_addr_internal is a GLIBC_PRIVATE private symbol on s390{,x}, the glibc folks aren't very happy about asan using it.
Additionally, only recent glibc versions have it, older versions just have __tls_get_offset and nothing else.
The patch doesn't drop the __tls_get_addr_internal interception altogether, but changes it so that it calls real __tls_get_offset function instead (and much more importantly,
that __tls_get_offset interception calls the real __tls_get_offset function).
This way it should work also on glibc 2.18 and earlier.  See http://gcc.gnu.org/PR79341 for further details.

Reviewers: kcc, koriakin

Reviewed By: kcc, koriakin

Subscribers: kubamracek, mehdi_amini

Tags: #sanitizers

Differential Revision: https://reviews.llvm.org/D29735

llvm-svn: 294790