安装或升级Cocoapods失败：Failed to build gem native extension

使用Cocoapods时报错，尝试升级也报错。

$ sudo gem install cocoapods
Building native extensions. This could take a while...
ERROR:  Error installing cocoapods:
	ERROR: Failed to build gem native extension.

    current directory: /Library/Ruby/Gems/2.6.0/gems/ffi-1.15.5/ext/ffi_c
/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 ./siteconf20220919-8448-1x4boqd.rb extconf.rb
mkmf.rb can't find header files for ruby at /System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/include/ruby.h

You might have to install separate package for the ruby development
environment, ruby-dev or ruby-devel for example.

extconf failed, exit code 1

Gem files will remain installed in /Library/Ruby/Gems/2.6.0/gems/ffi-1.15.5 for inspection.
Results logged to /Library/Ruby/Gems/2.6.0/extensions/universal-darwin-21/2.6.0/ffi-1.15.5/gem_make.out

之前一直是好的，这种情况可能是因为，系统未安装Xcode或未设置Xcode版本。另外，更新Xcode版本，也可能会导致Xcode设置重置。

# 查看当前的Xcode设置
$ xcode-select -p

可在Xcode / Preferences / Locations / Command Line Tools检查设置，或者通过下面的命令设置Xcode路径。

# 将 /Applications/Xcode.app 替换为实际路径
$ xcode-select --switch /Applications/Xcode.app