The ar file format is pretty simple and can be implemented by using a Go
library. Use that instead of calling out to llvm-ar.
There are a few limitations to the used package, but that doesn't seem
to matter for our use case (linking compiler-rt for use with ld.lld):
* no index is created
* long filenames are truncated
* no support for archives bigger than 4GB
This provides several advantages. Among others:
* Much faster and hopefully more reliable.
* Good caching support to store LLVM builds.
* Building and testing of release-ready artifacts.
LLD version 8 has added support for armv6m:
https://reviews.llvm.org/D55555
This means we can use LLD instead of arm-none-eabi-ld, eliminating our
dependency on GNU binutils.
There are small differences in code size, but never more than a few
bytes.
This commit does a few things:
* remove the -8 suffix on macOS, where it is not necessary
* add smoke tests for compiling wasm files on Linux and macOS
CircleCI is faster and has more features than Travis CI. Additionally,
based on the recent news, the future of Travis CI is rather uncertain.
Keep using Travis CI for macOS testing at the moment, as open source
projects will need to get special permission to use CircleCI for macOS
tests.
