https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88912
--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> --- #define TARGET_F951_OPTIONS "%{!nostdinc:\ %:fortran-preinclude-file(-fpre-include= math-vector-fortran.h finclude%s/)}" in config/gnu-user.h adds that if the file is found.