[BOLT][DWARF] Properly emit of end-of-sequence entries for line tables

Summary:
When the compiler emits line table program, it emits EOS using the label
at the end of the containing code section. Since each compilation unit
has its own set of code sections it works as expected (* see the excerpt
from the standard below). However, in BOLT the code from many CUs is
combined into a common section, such as hot text or cold text.
As a result, the symbol at the end of the section may point way past the
code sequence for a given unit.

Since we can emit functions in any order, we conservatively emit
end-of-sequence at the end of every emitted function.

Fixes a problem while intermixing source code with disassembly in
binutils' objdump.

(*) DWARF v4 6.2.5.3:
"Every line number program sequence must end with a DW_LNE_end_sequence
instruction which creates a row whose address is that of the byte after
the last target machine instruction of the sequence."

(cherry picked from FBD31347870)