Update build.sh

[tarnith]

Moved the hardcoded directory to at least C;\temp so the chance of overwriting existing files is reduced. Perhaps a check for existing directores before wiping data would be advised.

[CLAassistant]

All committers have signed the CLA.

[abique]

Did you confirm that the path was short enough to build qt using vcpkg?

[tarnith]

Can't confirm as can't complete build due to other build errors.

Perhaps a better PR would be a simple
if [ -d "/path/to/directory" ]; then echo "Directory exists. Delete or choose another buildtree" break

I notice some other build scripts also hard code C:\B which is unfortunately a preexisting folder on my system for other things requiring a short path.
vcpkgerror.log