leveldb: generate lib independent of locale sort #8575

This patch modifies src/leveldb/build_detect_platform to ensure that the sorted PORTABLE_FILES is collated in a canonical order and hence varying locale collation order will not cause generated objects to vary. Patch due to Reiner Herrmann from Debian's reproducible build project.

This patch is applied in the 0.12.1 and 0.13.0 builds I've done in Debian. The corresponding Debian bug report is at https://bugs.debian.org/791834 and reproducible build history is at https://tests.reproducible-builds.org/debian/history/bitcoin.html

Debian patch as applied can be seen at either:

http://sources.debian.net/src/bitcoin/0.12.1-0.1/debian/patches/1008_reproducible_build.patch http://sources.debian.net/src/bitcoin/0.13.0-0.1~exp1/debian/patches/1008_reproducible_build.patch

Good catch. For 0.13 and later this should be a no-op, though, as we no longer use leveldb's build system. See #7911.

I'm not sure how to handle this. As said, for 0.13 we don't specifically need it, and 0.12 likely won't get a leveldb subtree update anymore. However, merging this directly into the 0.12 branch is going to mess up future subtree updates if we do happen to need one.

In any case I think it would make sense to get this into upstream leveldb at https://github.com/google/leveldb.

Agree, I think you should propose this for upstream. If it goes in there, we'll include it in the next subtree update, but even then, that's unlikely to go in 0.12, which is the only place where it would matter.

If this isn't useful for master or 0.13, it doesn't seem worth worrying about? Given how long https://github.com/google/leveldb/pull/291 has been open, upstreaming doesn't seem likely...