Override the vcpkg/scripts/detect_compiler behavior of always pulling
$CC and $CXX at the time that vcpkg install is determined to need called
by forcing $ENV{CXX} and $ENV{CC} to our CMake-determined compiler.
This prevents strange behavior such as running the following:
./Meta/ladybird.sh run
make changes...
ninja -C Build/ladybird
Where the second build step would be run without CC or CXX set in the
environment, causing a total cache miss from vcpkg and a full rebuild.
It also helps prevent full rebuilds when an IDE passes a slightly
different compiler to the build step than ladybird.sh.
We currently build debug and release versions of vcpkg dependencies. We
will most commonly only need the release version, so let's default to
that to approximately halve our dependency build time.
