dependencies/pkgconfig: Log pkg-config exceptions
This means that when either cflags or libs lookup fails, this will be
logged always in the log, leading to much easier to debug messages
Called `/usr/local/bin/pkg-config --cflags gnutls` -> 1
pkg-config error with 'gnutls': Could not generate cargs for gnutls:
Package nettle was not found in the pkg-config search path.
Perhaps you should add the directory containing `nettle.pc'
to the PKG_CONFIG_PATH environment variable
Package 'nettle', required by 'gnutls', not found
Run-time dependency gnutls found: NO (tried pkgconfig)