Using VFLAGS, you can pass common options through it to the V compiler,
without having to manually specify them everytime when you type V ...
In addition, since environment variables are *inherited*, all subprocess
V compilers, which V launches (for example when compiling with -live),
will *also* use the same VFLAGS environment variable.
Example usage:
export VFLAGS="-debug -show_c_cmd"
v -live message.v
=> This will keep *both* of the generated C source files .message.c
*AND* .message_shared_lib.c . It will also cause both V compile
subprocesses to print their resulting C compiler backend lines.
This is very useful when using GDB to debug problems.