Set `ZIG_PIE` default to be same as `CMAKE_POSITION_INDEPENDENT_CODE`, and
add check for situation when `ZIG_PIE` is set to True but CMake does not
support compiling position independent code. CMake's support is needed
for "zigcpp" target.

Also remove temporary variables for constructing `ZIG_BUILD_ARGS`,
instead use `list(APPEND ...)` functions.

Also remove long unused `ZIG_NO_LANGREF` variable.

Signed-off-by: Eric Joldasov <bratishkaerik@landless-city.net>