[PATCH] Pass -mglobal-merge as a module flag metadata.

[Duncan P. N. Exon Smith]

> On 2015 Mar 1, at 14:11, Ahmed Bougacha <ahmed.bougacha at gmail.com> wrote:
> 
> And yes, in case that wasn't clear, conflicting flags should be an error.
> 

Why should we error on a difference here?  It makes more sense to me
to disable global merge if any module disables it.

We can get this behaviour by only specifying a module flag when
-mno-global-merge.