Warning: The install command is a part of the legacy v1 style of cabal usage.

Please switch to using either the new project style and the new-install
command or the legacy v1-install alias as new-style projects will become the
default in the next version of cabal-install. Please file a bug if you cannot
replicate a working v1- use case with the new-style commands.

For more information, see: https://wiki.haskell.org/Cabal/NewBuild

Resolving dependencies...
Starting     base16-bytestring-0.1.1.6
Starting     data-default-class-0.1.2.0
Building     base16-bytestring-0.1.1.6
Building     data-default-class-0.1.2.0
Completed    data-default-class-0.1.2.0
Completed    base16-bytestring-0.1.1.6
Downloading  toxcore-c-0.2.11
Downloaded   toxcore-c-0.2.11
Starting     toxcore-c-0.2.11
Failed to install toxcore-c-0.2.11
Build log ( /home/builder/.cabal/logs/ghc-8.6.3/toxcore-c-0.2.11-FCtWnQGWSxu4ha61puKaDT.log ):
cabal: Entering directory '/tmp/cabal-tmp-5031/toxcore-c-0.2.11'
Configuring toxcore-c-0.2.11...
cabal: Missing dependencies on foreign libraries:
* Missing (or bad) C libraries: toxcore, toxcore
This problem can usually be solved by installing the system packages that
provide these libraries (you may need the "-dev" versions). If the libraries
are already installed but in a non-standard location then you can use the
flags --extra-include-dirs= and --extra-lib-dirs= to specify where they are.If
the library files do exist, it may contain errors that are caught by the C
compiler at the preprocessing stage. In this case you can re-run configure
with the verbosity flag -v3 to see the error messages.

cabal: Leaving directory '/tmp/cabal-tmp-5031/toxcore-c-0.2.11'
cabal: Error: some packages failed to install:
toxcore-c-0.2.11-FCtWnQGWSxu4ha61puKaDT failed during the configure step. The
exception was:
ExitFailure 1