preproc: command-line preproc directive after system-generated

preproc: command-line preproc directive after system-generated

BR 3392527: make sure that all command-line specified preprocessing
directives are processed after the system-generated ones. In
particular __OUTPUT_FORMAT__ was generated after command line pass 2,
at which point -p, -d, -u, --pragma and --before had already been
processed.

There is no reason to split up defined_macros() anymore: the right
place to execute it is simply between command line passes 1 and 2. We
can also set dfmt here, which lets us define a __DEBUG_FORMAT__ macro
as well.

Finally move some options that have no business being processed in
pass 2 to pass 1.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>