make: Define default rule for .c when V=1 or V=2

The default .o:.c rule passes a short file name to gcc to when doing
"make -C <dir>", we do this a lot for all the libraries.
The file names printed in gcc errors are relative to <dir> and this
prevents vim from navigating through errors.

This passes the full file name to gcc to make it print errors with
absolute path so vim can navigate through errors nicely.

This makes it optional when V=1 or V=2 is passed.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>