Adding a "release" setting in build.mk.sample (and some other build system questions)

[Harry .]

> Date: Fri, 29 Jan 2016 17:44:56 +0100 
> Subject: Re: Adding a "release" setting in build.mk.sample (and some  
> other build system questions) 
> From: thomasmiedema at gmail.com 
> To: voldermort at hotmail.com 
> CC: ghc-devs at haskell.org 
>  
> The default (and thus release) `SRC_HC_OPTS` uses `-H32m` (see  
> mk/config.mk.in<http://config.mk.in>). 
>  
> Maybe you want to run some tests to see if it makes a difference on the  
> total build time? 
>  
> I suggest also measuring without any `-H` flag, with just `-H` (see  
> commit below), and with `-H1G` or some other large value. 

I'm building in a container on a busy host at work (i.e. which I don't control), so unfortunately there's too much background noise to make meaningful measurements.

Does SRC_HC_OPTS control memory usage while building GHC, or when it's running? And either way, why does this need setting for building GHC, but isn't normally used when compiling regular Haskell programs?