This PR introduces the following CMake-related improvements to contrib/guix/libexec/build.sh:
Drop redundant CMake
--verboseoptions, as verbose output is already controlled by theVERBOSEenvironment variable, which has been exported since 85f4a4b0822e3aa10310c4623eff719f301e9263.Fixes the "Ignoring empty string" CMake warning for non-Linux hosts.