[pph] Stream and merge line table. (issue4836050)

[Gabriel Charette]

[+ccoutant]

>> Added lto streamer hooks to do this, but Cary (ccoutant) was saying he'd
>> want it directly in lto.
>>
>> Do we want to apply the changes to libcpp to trunk now or wait??
>
> How urgent is the merge?  It wouldn't hurt to run a few more test
> cases.  I have some hidden in my client....


Neither the merge to lto (Cary said he'd like that), nor the libcpp
merge to trunk are required (libcpp changes are trivial, just pulling
out some inline code into a function for re-use and defined some
constants to avoid "magic numbers" in the code, but there is not much
point for them without the pph code (i.e. they'll only be used once
each, where they were originally pulled out from)).

Gab
We can definitely keep it in pph for a little while until it's stable.