[BOLT] Make sure all section allocations have deterministic contents

For empty sections, RuntimeDyld always allocates 1 byte but leaves it
uninitialized. This causes the contents of some output sections to be
non-deterministic.

Note that this issue is also solved by D147544.

Fixes #59008

Reviewed By: maksfb

Differential Revision: https://reviews.llvm.org/D149243