llvm: add mlir

[carlocab]

There's been some interest in the flang compiler for llvm:

Homebrew/discussions#143
#63081

It seems possible to build flang separately from llvm, but it appears to
require having built mlir. See the flang README. Aside from being a
pre-requisite for flang, mlir is a mature project with a number of
interesting applications.

mlir, therefore, seems worthy of inclusion in the llvm formula even if
flang is currently not suitable for homebrew/core. (flang does build
and test successfully upon declaring a dependency on llvm in this PR.)

Test failure appears to be unrelated to the PR, and has been reported
upstream: odin-lang/Odin#792

---

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[carlocab]

This is the error in the log archive:

❯ cat test.01.odin
2020-11-25 05:22:08 +0000

/usr/local/Cellar/odin/0.13.0/bin/odin
build
hellope.odin

ld: library not found for -lc

Error from the raw logs

An exception occurred within a child process:
  Errno::ENOENT: No such file or directory - ./hellope
/usr/local/Homebrew/Library/Taps/homebrew/homebrew-core/Formula/odin.rb:49:in ``'
/usr/local/Homebrew/Library/Taps/homebrew/homebrew-core/Formula/odin.rb:49:in `block in <class:Odin>'
/usr/local/Homebrew/Library/Homebrew/formula.rb:1872:in `block (3 levels) in run_test'
/usr/local/Homebrew/Library/Homebrew/utils.rb:500:in `with_env'
/usr/local/Homebrew/Library/Homebrew/formula.rb:1871:in `block (2 levels) in run_test'
/usr/local/Homebrew/Library/Homebrew/formula.rb:910:in `with_logging'
/usr/local/Homebrew/Library/Homebrew/formula.rb:1870:in `block in run_test'
/usr/local/Homebrew/Library/Homebrew/mktemp.rb:63:in `block in run'
/usr/local/Homebrew/Library/Homebrew/mktemp.rb:63:in `chdir'
/usr/local/Homebrew/Library/Homebrew/mktemp.rb:63:in `run'
/usr/local/Homebrew/Library/Homebrew/formula.rb:2114:in `mktemp'
/usr/local/Homebrew/Library/Homebrew/formula.rb:1864:in `run_test'
/usr/local/Homebrew/Library/Homebrew/test.rb:43:in `block in <main>'
/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/timeout.rb:93:in `block in timeout'
/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/timeout.rb:33:in `block in catch'
/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/timeout.rb:33:in `catch'
/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/timeout.rb:33:in `catch'
/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/timeout.rb:108:in `timeout'
/usr/local/Homebrew/Library/Homebrew/test.rb:42:in `<main>'

This error is not related to the PR:

Testing Odin under the existing llvm formula produces what looks to be the same error.

❯ brew install odin && brew test odin
==> Downloading https://homebrew.bintray.com/bottles/odin-0.13.0.catalina.bottle.tar.gz
==> Downloading from https://d29vzk4ow07wi7.cloudfront.net/772509e10bf0a73af78b51e4f85309eb6d25e0078d1f2fa02bfa2d252e0055ca?respons
######################################################################## 100.0%
==> Pouring odin-0.13.0.catalina.bottle.tar.gz
🍺  /usr/local/Cellar/odin/0.13.0: 133 files, 2.6MB
==> Testing odin
==> /usr/local/Cellar/odin/0.13.0/bin/odin version
==> /usr/local/Cellar/odin/0.13.0/bin/odin build hellope.odin
Error: odin: failed
An exception occurred within a child process:
  Errno::ENOENT: No such file or directory - ./hellope
/usr/local/Homebrew/Library/Taps/homebrew/homebrew-core/Formula/odin.rb:49:in ``'
/usr/local/Homebrew/Library/Taps/homebrew/homebrew-core/Formula/odin.rb:49:in `block in <class:Odin>'
/usr/local/Homebrew/Library/Homebrew/formula.rb:1862:in `block (3 levels) in run_test'
/usr/local/Homebrew/Library/Homebrew/utils.rb:500:in `with_env'
/usr/local/Homebrew/Library/Homebrew/formula.rb:1861:in `block (2 levels) in run_test'
/usr/local/Homebrew/Library/Homebrew/formula.rb:900:in `with_logging'
/usr/local/Homebrew/Library/Homebrew/formula.rb:1860:in `block in run_test'
/usr/local/Homebrew/Library/Homebrew/mktemp.rb:63:in `block in run'
/usr/local/Homebrew/Library/Homebrew/mktemp.rb:63:in `chdir'
/usr/local/Homebrew/Library/Homebrew/mktemp.rb:63:in `run'
/usr/local/Homebrew/Library/Homebrew/formula.rb:2104:in `mktemp'
/usr/local/Homebrew/Library/Homebrew/formula.rb:1854:in `run_test'
/usr/local/Homebrew/Library/Homebrew/test.rb:43:in `block in <main>'
/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/timeout.rb:93:in `block in timeout'
/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/timeout.rb:33:in `block in catch'
/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/timeout.rb:33:in `catch'
/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/timeout.rb:33:in `catch'
/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/timeout.rb:108:in `timeout'
/usr/local/Homebrew/Library/Homebrew/test.rb:42:in `<main>'

See also: #65000 (comment)

[BrewTestBot]

@fxcoudert has triggered a merge.

[fxcoudert]

Not sure I understand why calling make through cmake works when calling make directly doesn't, but I don't think it can hurt. (Using ninja, on the other hand, has in the past lead to a huge increase in our binary size, so we don't want that)

[carlocab]

Yup, I really don't get it either. Who knows what's inside llvm's build scripts...

I experimented building with Ninja too, and it's not as bad as it used to be (~3GB install), but still worse than just Make.

Thanks!