maintenance/talks/2023-dfn/demo.org

$ guix build hello
/gnu/store/5mqwac3zshjjn1ig82s12rbi7whqm4n8-hello-2.12.1

$ guix build hello --with-patch=hello=hello.patch
/gnu/store/3pryp1g7njm3zs9icq576zy8sf9sn6af-hello-2.12.1

$ guix build hello --with-configure-flag=hello=--with-packager=rekado
/gnu/store/9siab04l7zmaykn0mqm8wx7fgr4s5a00-hello-2.12.1

$ guix build hello --with-c-toolchain=hello=gcc@11
/gnu/store/p172s3bgyi42dnw174qnfglmjy0mnfnx-hello-2.12.1