How to write a SPEC function that gets all arguments passed?

[Georg Lay <avr at gjlay dot de>]

Hi, when calling gcc with -frecord-gcc-switch the options passed to cc1
will differ depending on if -save-temps is present or not. E.g. if
calling gcc foo.c -I Z -DX=... -UY ...
in the forst case (with -save-temps) options_passed is: "-fpreprocessed
foo.i ..."
in the second case (without -save-temps) options_passed is: "-IZ
-isystem ... -iprefix ... -DX=... -UY foo.c ..."

What is relevant to the user is the second string because that is the
way he calls gcc. What's internally going on when -save-temps is present
should be transparent. Therefore, I am looking for a way to pass the
arguments from gcc to cc1 and tried to implement this with the help of
some spec function. But I could not find out how to actually write down
the specs.

My idea was to add a spec function to DRIVER_SELF_SPECS that collects
all options and passes them as a string to cc1, but there seem to be no
way to call the function like
   %{*:%:my_record_switches(%*)}
or
   %:my_record_switches(%(cpp_options))

I also tries to use the %Z that collects all options but eigher I get
NULL as input or the thing crashes.
 
What am I missing?
Moreover, there will be a problem because the C function that actually
implements my_record_switches must return a string starting with '-',
there is no way to return "" or NULL to indicate that the function won't
produce anything.

Would anyone guide me through that specs jungle?

Georg