vte: Depend on system provided fmt package

vte: Depend on system provided fmt package

vte 0.82+ has started to package fmt as a subproject if this is not found
on system, the bundled version however, does not work with clang on
32bit machines, since it is 11.0 and there are fixes in newer version
needed to work with clang

Fixes
../sources/vte-0.82.1/subprojects/fmt/include/fmt/format.h:752:35: error: call to function 'free' that is neither visible in the template

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Cc: Gyorgy Sarvari <skandigraun@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>