[Bug preprocessor/71681] header.gcc file lookup is broken for -remap

[andris.pavenis at iki dot fi]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71681

--- Comment #1 from Andris Pavenis <andris.pavenis at iki dot fi> ---
Created attachment 38781
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=38781&action=edit
Fix for problem