linux-libc-dev:i386 is not produced anymore

[Thadeu Lima de Souza Cascardo]

[Impact]
On Bionic, after i386 and other architectures were dropped from building, linux-libc-dev:i386 stopped being produced. That stills needs to be produced for userspace multi-arch support. Otherwise installing newer linux-libc-dev binaries will remove the i386 version of it, as they need to be the same version.

[Test case]
Install linux-libc-dev and linux-libc-dev:i386 prepared by the same source package.

[Potential regression]
Packages may fail to build or different config options may be enabled.

[Ubuntu Kernel Bot (ubuntu-kernel-bot)]

This bug is awaiting verification that the linux-azure/4.15.0-1170.185~14.04.1 kernel in -proposed solves the problem. Please test the kernel and update this bug with the results. If the problem is solved, change the tag 'verification-needed-trusty-linux-azure' to 'verification-done-trusty-linux-azure'. If the problem still exists, change the tag 'verification-needed-trusty-linux-azure' to 'verification-failed-trusty-linux-azure'.

If verification is not done by 5 working days from today, this fix will be dropped from the source code, and this bug will be closed.

See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how to enable and use -proposed. Thank you!