[BOLT] Fix writing out unmarked .eh_frame section

[BOLT] Fix writing out unmarked .eh_frame section

When BOLT updates .eh_frame section, it concatenates newly-generated
contents (from CFI directives) with the original .eh_frame that has
relocations applied to it. However, if no new content is generated,
the original .eh_frame has to be left intact. In that case, BOLT was
still writing out the relocatable copy of the original .eh_frame section
to the new segment, even though this copy was never used and was not
even marked in the section header table.

Detect the scenario above and skip allocating extra space for .eh_frame.

Reviewed By: rafauler

Differential Revision: https://reviews.llvm.org/D135223