Michael Voorhaen

I've got the same issue after upgrading to MacOS 11 Big Sur: ``` > cat /Library/Ruby/Gems/2.6.0/extensions/universal-darwin-20/2.6.0/clocale-0.0.4/mkmf.log "xcrun clang -o conftest -I/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.15.sdk/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/include/ruby-2.6.0/universal-darwin20 -I/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.15.sdk/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/include/ruby-2.6.0/ruby/backward -I/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.15.sdk/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/include/ruby-2.6.0 -I. -D_XOPEN_SOURCE -D_DARWIN_C_SOURCE -D_DARWIN_UNLIMITED_SELECT -D_REENTRANT -g -Os...

In my case, since I just updated to MacOS Big Sur, it turns out that I needed to update XCode. After the update finished, I was able to install the...