[Bug target/40411] -std=c99 does not enable c99 mode in Solaris C library

[ro at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=40411

--- Comment #30 from Rainer Orth <ro at gcc dot gnu.org> ---
Created attachment 40507
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=40507&action=edit
combined proposed patch