[BUG] ZenC doesn't pass ZC_ROOT to C compiler

[borup3]

Describe the bug
Examples can't be built from other than the root Zen-C directory because ZenC doesn't pass ZC_ROOT to the C compiler, presumably.

This results in e.g. binsearch.zc being unable to build if zc is invoked from its own directory, due to the relative include output into the C file:

#include "std/third-party/tre/include/tre.h"

To Reproduce
Steps to reproduce the behavior:

1. Set working directory to examples/examples/internal/algorithms
2. zc run binsearch.zc
3. See include path error

Expected behavior
zc should pass ZC_ROOT to the C compiler to it can find std/ include paths.

[Zuhaitz-dev]

It should work fine now. If you find similar issues, please report them.