Fix for rL280668, Intel(R) Memory Protection Extensions (Intel(R) MPX) support.

Summary: Signed-off-by: Valentina Giusti <valentina.giusti@intel.com>

Reviewers: dvlahovski, granata.enrico, clayborg, labath

Subscribers: lldb-commits

Differential Revision: https://reviews.llvm.org/D24255

llvm-svn: 280942