Example of debugging GCC with toplevel bootstrap

[Paolo Bonzini]

>>    make all-stage2 STAGE1_LANGUAGES=c,fortran
>>
>So, how would I now get a cc1plus/f951/jc1/cc1 binary compiled by the 
>stage0 (host) compiler?
>
>That would give me the 4 '-g -O0' binaries compiled with the system 
>compiler.  I've tried following these notes, but it always gives me 
>binaries built by 'prev-gcc/xgcc'.
>  
>
My notes were for a miscompilation, so I also needed the stage2 
binaries, built by prev-gcc/xgcc.

make stage1-bubble STAGE1_LANGUAGES=c,c++,fortran,java

I think that after I fix PR25670, as a side effect, you will also be 
able to use the more intuitive target "all-stage1".  But I didn't think 
of that PR much closely because it is about a target that was anyway 
undocumented, and there are bigger fish to fry.

Paolo