MacOS 10.15 执行bundle install，安装到byebug时报错，信息如下：
Installing byebug 11.1.3 with native extensions
Gem::Ext::BuildError: ERROR: Failed to build gem native extension.
current directory:
/private/var/folders/t4/qywk21kj3xzc57q97zhkx9980000gn/T/bundler20210406-33219-n8qsf0byebug-11.1.3/gems/byebug-11.1.3/ext/byebug
/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/bin/ruby -I
/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0 -r
./siteconf20210406-33219-1p5ofqz.rb extconf.rb
creating Makefile
current directory:
/private/var/folders/t4/qywk21kj3xzc57q97zhkx9980000gn/T/bundler20210406-33219-n8qsf0byebug-11.1.3/gems/byebug-11.1.3/ext/byebug
make "DESTDIR=" clean
current directory:
/private/var/folders/t4/qywk21kj3xzc57q97zhkx9980000gn/T/bundler20210406-33219-n8qsf0byebug-11.1.3/gems/byebug-11.1.3/ext/byebug
make "DESTDIR="
make: *** No rule to make target
`/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/include/ruby-2.6.0/universal-darwin19/ruby/config.h',
needed by `breakpoint.o'. Stop.
make failed, exit code 2
Gem files will remain installed in
/var/folders/t4/qywk21kj3xzc57q97zhkx9980000gn/T/bundler20210406-33219-n8qsf0byebug-11.1.3/gems/byebug-11.1.3
for inspection.
Results logged to
/var/folders/t4/qywk21kj3xzc57q97zhkx9980000gn/T/bundler20210406-33219-n8qsf0byebug-11.1.3/extensions/universal-darwin-19/2.6.0/byebug-11.1.3/gem_make.out
An error occurred while installing byebug (11.1.3), and Bundler cannot
continue.
Make sure that `gem install byebug -v '11.1.3' --source 'https://rubygems.org/'`
succeeds before bundling.
看样子是找不到header，在~/.bash_profile中添加环境变量如下：
SDKROOT=/Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk/
export SDKROOT
如果你的系统不是10.15，可以试试同级目录中类似命名的文件夹。
如果没有类似文件夹，需要先使用xcode-select --install安装Xcode开发工具。
source ~/.bash_profile刷新环境变量后，再执行bundle install就没问题了。
