unable to install: dependency unf_ext 0.0.7.5 ERROR failed to build gem native extension

[twitterkb]

trying to migrate from xcpretty to trainer in order to parallelize unit tests on CI.

have very few other gems installed.

when i attempt to install trainer, it makes it through some portion of the gem installation, but then encounters the following.

Fetching unf_ext 0.0.7.5
Installing unf_ext 0.0.7.5 with native extensions
Gem::Ext::BuildError: ERROR: Failed to build gem native extension.
current directory: /x/beta/.gems/gems/unf_ext-0.0.7.5/ext/unf_ext /System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/bin/ruby -r ./siteconf20190307-81514-nw7co1.rb extconf.rb
checking for main() in -lstdc++... *** extconf.rb failed ***

not clear from the Readme.md or any other documentation here what pre-requisites are required prior to performing this gem install.

[pyby]

I had the same issue on Mac OS Mojave and Xcode 11.2 and unf_ext 0.0.7.6.
To fix it, I downgraded Xcode command line tools to Xcode 10.3 and bundle install worked as expected.