Problem updating Cocoa Pods on OSX 10.12.6 - cocoapods

Question

I'm trying to update cocoa pods in order to build an iOS version of an Ionic/Capacitor project but I keep getting the following error:
ERROR: Failed to build gem native extension.
I tried uninstalling and reinstalling, but no joy. I also tried the troubleshooting options on the cocoa pods site.
More info:
current directory: /Library/Ruby/Gems/2.3.0/gems/ffi-1.12.2/ext/ffi_c
/System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/bin/ruby -r ./siteconf20200415-1988-1gtlurs.rb extconf.rb
checking for ffi.h... *** 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/2.3/usr/bin/$(RUBY_BASE_NAME)
--with-ffi_c-dir
--without-ffi_c-dir
--with-ffi_c-include
--without-ffi_c-include=${ffi_c-dir}/include
--with-ffi_c-lib
--without-ffi_c-lib=${ffi_c-dir}/lib
--enable-system-libffi
--disable-system-libffi
--with-libffi-config
--without-libffi-config
--with-pkg-config
--without-pkg-config
/System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/2.3.0/mkmf.rb:456: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/2.3/usr/lib/ruby/2.3.0/mkmf.rb:571:in `block in try_compile'
from /System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/2.3.0/mkmf.rb:524:in `with_werror'
from /System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/2.3.0/mkmf.rb:571:in `try_compile'
from /System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/2.3.0/mkmf.rb:1091:in `block in have_header'
from /System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/2.3.0/mkmf.rb:942:in `block in checking_for'
from /System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/2.3.0/mkmf.rb:350:in `block (2 levels) in postpone'
from /System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/2.3.0/mkmf.rb:320:in `open'
from /System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/2.3.0/mkmf.rb:350:in `block in postpone'
from /System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/2.3.0/mkmf.rb:320:in `open'
from /System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/2.3.0/mkmf.rb:346:in `postpone'
from /System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/2.3.0/mkmf.rb:941:in `checking_for'
from /System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/2.3.0/mkmf.rb:1090:in `have_header'
from extconf.rb:10:in `system_libffi_usable?'
from extconf.rb:34:in `<main>'
Log file:
package configuration for libffi is not found
"xcrun clang -o conftest -I/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.13.sdk/System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/include/ruby-2.3.0/universal-darwin16 -I/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.13.sdk/System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/include/ruby-2.3.0/ruby/backward -I/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.13.sdk/System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/include/ruby-2.3.0 -I. -D_XOPEN_SOURCE -D_DARWIN_C_SOURCE -D_DARWIN_UNLIMITED_SELECT -D_REENTRANT -g -Os -pipe -DHAVE_GCC_ATOMIC_BUILTINS -iwithsysroot /usr/local/libressl/include conftest.c -L. -L/System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib -L. -L /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.12.Internal.sdk/usr/local/libressl/lib -L/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.12.Internal.sdk/usr/local/lib -arch x86_64 -arch i386 -lruby.2.3.0 -lpthread -ldl -lobjc "
In file included from conftest.c:1:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.13.sdk/System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/include/ruby-2.3.0/ruby.h:33:
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.13.sdk/System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/include/ruby-2.3.0/ruby/ruby.h:24:10: fatal error: 'ruby/config.h' file not found
#include "ruby/config.h"
^~~~~~~~~~~~~~~
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 */