b919efadff depends: Use default macos clang compiler (Russell Yanofsky)
d54f64c6c7 Add multiprocess travis configuration (Russell Yanofsky)
787f40668d Set LD_LIBRARY_PATH consistently in travis tests (Russell Yanofsky)
d630646662 libmultiprocess depends build (Russell Yanofsky)
e6e44eedd5 Multiprocess build changes (Russell Yanofsky)
Pull request description:
This PR is part of the [process separation project](https://github.com/bitcoin/bitcoin/projects/10).
This splits autotools, depends build, and travis changes out of #10102, so code changes and build system changes can be reviewed separately.
ACKs for top commit:
hebasto:
re-ACK b919efadff, rebased only since my [previous](https://github.com/bitcoin/bitcoin/pull/16367#issuecomment-605514556) review.
Tree-SHA512: ebc5e403cc99a0d9629ed7fe1595e01d57e6d1255cbf03968a3196ff6f528f734c78060fdc065724ee1f923bcc5aa2b29470fcb36a7f15957eb57c76d58178a4