Can't install Squib on macOS. "ruby/config.h" not found

[ElectricCoffee]

Trying to install squib via gem install. My currently installed version of Ruby is 2.6.10.

This is the output I get from the console when trying to do this:

Fetching red-colors-0.4.0.gem
Fetching pkg-config-1.5.6.gem
Fetching native-package-installer-1.1.9.gem
Fetching cairo-1.17.13.gem
Fetching glib2-4.2.1.gem
Fetching cairo-gobject-4.2.1.gem
Fetching gobject-introspection-4.2.1.gem
Fetching ruby-progressbar-1.13.0.gem
Fetching gio2-4.2.1.gem
Fetching gdk_pixbuf2-4.2.1.gem
Fetching rsvg2-4.2.1.gem
Fetching rubyzip-2.3.2.gem
Fetching racc-1.7.3.gem
Fetching nokogiri-1.16.2-x86_64-darwin.gem
Fetching roo-2.10.1.gem
Fetching rainbow-3.1.1.gem
Fetching pango-4.2.1.gem
Fetching mercenary-0.4.0.gem
Fetching highline-2.1.0.gem
Fetching classy_hash-1.0.0.gem
Fetching squib-0.19.0.gem
Successfully installed ruby-progressbar-1.13.0
Successfully installed native-package-installer-1.1.9
Successfully installed pkg-config-1.5.6
Building native extensions. This could take a while...
ERROR:  Error installing squib:
	ERROR: Failed to build gem native extension.

    current directory: /Library/Ruby/Gems/2.6.0/gems/glib2-4.2.1/ext/glib2
/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 ./siteconf20240223-7112-1r5x9kp.rb extconf.rb
checking for --enable-debug-build option... no
checking for -Wall option to compiler... *** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of necessary
libraries and/or headers.  Check the mkmf.log file for more details.  You may
need configuration options.

Provided configuration options:
	--with-opt-dir
	--without-opt-dir
	--with-opt-include
	--without-opt-include=${opt-dir}/include
	--with-opt-lib
	--without-opt-lib=${opt-dir}/lib
	--with-make-prog
	--without-make-prog
	--srcdir=.
	--curdir
	--ruby=/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/bin/$(RUBY_BASE_NAME)
	--enable-debug-build
	--disable-debug-build
/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/mkmf.rb:467:in `try_do': The compiler failed to generate an executable file. (RuntimeError)
You have to install development tools first.
	from /System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/mkmf.rb:585:in `block in try_compile'
	from /System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/mkmf.rb:534:in `with_werror'
	from /System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/mkmf.rb:585:in `try_compile'
	from /Library/Ruby/Gems/2.6.0/gems/glib2-4.2.1/lib/mkmf-gnome.rb:65:in `block in try_compiler_option'
	from /System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/mkmf.rb:959:in `block in checking_for'
	from /System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/mkmf.rb:361:in `block (2 levels) in postpone'
	from /System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/mkmf.rb:331:in `open'
	from /System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/mkmf.rb:361:in `block in postpone'
	from /System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/mkmf.rb:331:in `open'
	from /System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/mkmf.rb:357:in `postpone'
	from /System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/mkmf.rb:958:in `checking_for'
	from /Library/Ruby/Gems/2.6.0/gems/glib2-4.2.1/lib/mkmf-gnome.rb:64:in `try_compiler_option'
	from /Library/Ruby/Gems/2.6.0/gems/glib2-4.2.1/lib/mkmf-gnome.rb:74:in `<top (required)>'
	from /System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/rubygems/core_ext/kernel_require.rb:54:in `require'
	from /System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/rubygems/core_ext/kernel_require.rb:54:in `require'
	from extconf.rb:27:in `<main>'

To see why this extension failed to compile, please check the mkmf.log which can be found here:

  /Library/Ruby/Gems/2.6.0/extensions/universal-darwin-21/2.6.0/glib2-4.2.1/mkmf.log

extconf failed, exit code 1

Gem files will remain installed in /Library/Ruby/Gems/2.6.0/gems/glib2-4.2.1 for inspection.
Results logged to /Library/Ruby/Gems/2.6.0/extensions/universal-darwin-21/2.6.0/glib2-4.2.1/gem_make.out

In the mkmf.log file mentioned I have this bit of info:

checking for --enable-debug-build option... -------------------- no

--------------------

"xcrun clang -o conftest -I/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX13.1.sdk/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/include/ruby-2.6.0/universal-darwin21 -I/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX13.1.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/MacOSX13.1.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 -pipe -DHAVE_GCC_ATOMIC_BUILTINS -DUSE_FFI_CLOSURE_ALLOC conftest.c  -L. -L/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib -L. -L/AppleInternal/Library/BuildRoots/bc10cbcd-3cda-11ee-b8ac-16228a05f5d2/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX12.7.Internal.sdk/usr/local/lib     -lruby.2.6   "
In file included from conftest.c:1:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX13.1.sdk/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/include/ruby-2.6.0/ruby.h:33:
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX13.1.sdk/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/include/ruby-2.6.0/ruby/ruby.h:24:10: fatal error: 'ruby/config.h' file not found
#include "ruby/config.h"
         ^~~~~~~~~~~~~~~
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX13.1.sdk/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/include/ruby-2.6.0/ruby/ruby.h:24:10: note: did not find header 'config.h' in framework 'ruby' (loaded from '/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/System/Library/Frameworks')
1 error generated.
checked program was:
/* begin */
1: #include "ruby.h"
2: 
3: int main(int argc, char **argv)
4: {
5:   return 0;
6: }
/* end */

It appears ruby/config.h can't be found, preventing compilation.

I've had this issue on two different macs.

What do I do?