Builds currently fail with `ar` trying to operate on what are clearly
two paths concatenated together. It stems from a backward-incompatible
change in Make:
> Previously appending using '+=' to an empty variable would result in
> a value starting with a space. Now the initial space is only added
> if the variable already contains some value. Similarly, appending an
> empty string does not add a trailing space.
This issue was first reported on the MAME repository proper
(https://github.com/mamedev/mame/issues/6248), and affects libretro's
2016 snapshot as well. A fix that is reported to work with previous
versions of Make was upstreamed to:
- GENie, the build system: https://github.com/bkaradzic/GENie/pull/493
- MAME: https://github.com/mamedev/mame/pull/6262
- libretro: https://github.com/libretro/mame2016-libretro/pull/47
The fetched patch comes from the last of these.
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