Do not suggest debug = TRUE if it was already given

[gaborcsardi]

> pkgbuild::check_build_tools(debug = TRUE)
Trying to compile a simple C file
Error: Could not find tools necessary to compile a package
Call `pkgbuild::check_build_tools(debug = TRUE)` to diagnose the problem.
Error: Could not find tools necessary to compile a package

[hadley]

Is it also supposed to give more output when debug = TRUE.