Detect early if an UTF-8 locale is needed

Check in toolchain/dependencies/dependencies.sh if an UTF-8 locale is
properly present on the system before trying to build a locale enabled
toolchain. As this test is only needed when a locale enabled toolchain
is going to be built, we pass the configuration file path to the
dependencies.sh script so that it can grep for the current value of
various options.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>