config.mk.in: Disable stripping by default on ARM

Authored by bgamari.

Description

config.mk.in: Disable stripping by default on ARM

The Cortex A8 hardware apparently has a bug which ld.gold will try to
correct; however in order to do so it must have unstripped executables
lest we see warnings of the form (see Trac #10376, Trac #10464),

/usr/bin/ld.gold: warning: cannot scan executable section 1 of ...
for Cortex-A8 erratum because it has no mapping symbols.

Consequently we disabling stripping by default on this architecture.

A bit more discussion about this issue can be found in this Android issue.

Test Plan: Try validating on ARM

Reviewers: erikd, austin, thomie

Reviewed By: austin, thomie

Differential Revision: https://phabricator.haskell.org/D1599

GHC Trac Issues: Trac #10376, Trac #10464