stage2: use execve where available for zig test and zig run
stage2: use execve where available for zig test and zig run

closes #6531

zig-lang/zig,raulgrell/zig,raulgrell/zig,andrewrk/zig,zig-lang/zig,raulgrell/zig,raulgrell/zig,raulgrell/zig,andrewrk/zig,zig-lang/zig