[mmp] Need libmono-system-native.a support

[chamons]

Mono has introduced a new libmono-system-native.a library that mmp needs to know about. If you build some projects linking against System mono you will see this on new mono (5.18):

  Undefined symbols for architecture x86_64: (TaskId:394)
    "_mono_pal_init", referenced from: (TaskId:394)
       -u command line option (TaskId:394)
ld: symbol(s) not found for architecture x86_64 (TaskId:394)

This was introduced in a mono that is shipping with d16-0-p1, so the fix will need to be applied there as well.

[spouliot]

d16-0-p1 was branched before mono 2018-06 was merged, i.e. only master is affected.
P2 will be branched from master, so the fix is needed before that.

[spouliot]

@chamons I think you forgot to link #4980 to this bug ? (or there was another part ?!?)

[chamons]

Guilty as charged.

I commented on the PR which is the best I think I can do at this point.