[BOLT][perf2bolt] Fix base address calculation for shared objects

When processing profile data for shared object or PIE, perf2bolt needs
to calculate base address of the binary based on the map info reported
by the perf tool. When the mapping data provided is for the second
(or any other than the first) segment and the segment's file offset
does not match its memory offset, perf2bolt uses wrong assumption
about the binary base address.

Add a function to calculate binary base address using the reported
memory mapping and use the returned base for further address
adjustments.

Reviewed By: yota9

Differential Revision: https://reviews.llvm.org/D123755