Support bitcode for Apple platforms

[keith]

This changes the osx crosstool to support bitcode for all apple
platforms.

The behavior of bitcode is:

• For simulators, never pass any bitcode related linker, or compiler flags
• For devices:
  • For embedded bitcode markers
    • Pass -fembed-bitcode-marker to the compile and link commands
  • For embedded bitcode
    • Pass -fembed-bitcode to the compile and link commands
    • Pass -bitcode_verify -bitcode_hide_symbols -bitcode_symbol_map to the link command
    • Pass a output file path, wrapped in BITCODE_TOUCH_SYMBOL_MAP which is a clang wrapper workaround

With any bitcode link commands, you cannot pass -headerpad_max_install_names or you get a warning. You can see the logic for that here. To make sure that debug and release builds are as close as possible, I've disabled this flag for all builds including the simulator if bitcode is requested.

Fixes #4982

[keith]

@sergiocampama @thomasvl if you could take a look that would be great!

[rajivshah3]

Related: bazelbuild/rules_apple#163

[keith]

It also looks like after pulling this commit broke my change 71bc38f

It seems that I might have to regenerate that file

[keith]

@trybka do you know if I should be editing that new file instead? I ran the migrator but it results in a significantly different file // @scentini

[scentini]

Yes, you should be editing the new file instead, sorry for the confusion, I'll go ahead and erase the CROSSTOOL files and templates now.
Let me know if you need help with converting your features to Starlark code.

[keith]

I've updated this PR, @trybka it would be awesome if you could take another look at the logic now, @scentini if you have a minute it would be great if you could verify I followed the best practices with the new format.

Thanks!

[keith]

In the meantime here's an example of a rule that can be used to propagate these linker flags correctly for multi arch binaries ios-bazel-users/ios-bazel-users#14

[keith]

@trybka can you review the update?

[aragos]

I'll get this imported.

[keith]

Awesome thank you!

…

-- Keith Smiley

On Feb 13, 2019, at 11:09, aragos ***@***.***> wrote: @aragos approved this pull request. I'll get this imported. — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub, or mute the thread.

[keith]

Thanks!

[rajivshah3]

Thanks @keith !

[thii]

Can this feature be enabled/disabled with different cpus/platforms? We're not building with bitcode, but we have a watch app and building with bitcode is mandatory for watch apps.

[rajivshah3]

#10061 might help with that, but it's not implemented yet unfortunately

[keith]

In your ios_application target you might be able to do some features = ["-something"] to exclude this, although all the libraries would still be built with bitcode in that case, which may not be what you want.

[thii]

hmm... features = ["-bitcode_embedded"] doesn't seem to remove the bitcode linker flags. Any ideas?

[keith]

huh yea that's what I would have tried, I wonder if those features aren't passed through to the binaries from ios_application targets since it's a macro?