Building fails with Mac 14, Xcode 11.2, ruby 2.3.7

[jayshah123]

When running bundle install with following, error occurs...
Xcode 11.2.1
Build version 11B500
macOS 10.14.6
ruby version ruby 2.3.7p456 (2018-03-28 revision 63024) [universal.x86_64-darwin18]
Bundler version 2.1.4

Installing unf_ext 0.0.7.7 with native extensions
Gem::Ext::BuildError: ERROR: Failed to build gem native extension.

current directory:
/Users/myteam/.jenkins/workspace/myapp-fastlane-distribution/myaap/ios/vendor/bundle/ruby/2.3.0/gems/unf_ext-0.0.7.7/ext/unf_ext
/System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/bin/ruby -r
./siteconf20200421-10002-1r7wtfv.rb extconf.rb
mkmf.rb can't find header files for ruby at
/System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/include/ruby.h

extconf failed, exit code 1

Gem files will remain installed in
/Users/myteam/.jenkins/workspace/myapp-fastlane-distribution/myaap/ios/vendor/bundle/ruby/2.3.0/gems/unf_ext-0.0.7.7
for inspection.
Results logged to
/Users/myteam/.jenkins/workspace/myapp-fastlane-distribution/myaap/ios/vendor/bundle/ruby/2.3.0/extensions/universal-darwin-18/2.3.0/unf_ext-0.0.7.7/gem_make.out

An error occurred while installing unf_ext (0.0.7.7), and Bundler cannot
continue.
Make sure that `gem install unf_ext -v '0.0.7.7' --source
'https://rubygems.org/'` succeeds before bundling.

In Gemfile:
  fastlane was resolved to 2.145.0, which depends on
    faraday-cookie_jar was resolved to 0.0.6, which depends on
      http-cookie was resolved to 1.0.3, which depends on
        domain_name was resolved to 0.5.20190701, which depends on
          unf was resolved to 0.1.4, which depends on
            unf_ext

[Krishna]

I was running into the same problem (on macOS Catalina 10.15.3 (19D76), Xcode 11.4 (11E146)).

My fix was to do the following in the shell:

$ export SDKROOT="$(xcrun --sdk macosx --show-sdk-path)"
$ gem install unf_ext -v '0.0.7.5'

This worked for me.

I got the information about exporting SDKRoot from here.

Hope this helps someone.