Add a command to access and manipulate the Intel(R) MPX Boundary Tables.

Summary:
The Boundary Table Entries are stored in the application memory and allow
to store boundary info for all the pointers of the program, also those that
otherwise wouldn't fit in the 4 bound registers provided by the HW.

Here is an example of how it works:
 * mpx-table show <pointer>
        lbound = 0x..., ubound = 0x..., (pointer value = 0x..., metadata = 0x...)
 * mpx-table set <pointer>

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

Reviewers: labath, clayborg

Reviewed By: clayborg

Subscribers: lldb-commits, mgorny

Differential Revision: https://reviews.llvm.org/D29078

llvm-svn: 293660