--print-errors
If one or more of the modules on the command line, or their dependencies, are not found, or if an error
occurs in parsing a .pc file, then this option will cause errors explaining the problem to be printed.
With "predicate" options such as "--exists" pkg-config runs silently by default, because it's usually
used in scripts that want to control what's output. This option can be used alone (to just print errors
encountered locating modules on the command line) or with other options. The PKG_CONFIG_DEBUG_SPEW envi‐
ronment variable overrides this option.
from pkg-config man page: