[Bug c/68657] [6 Regression] "gcc -Werror=sign-conversion test.i" shows invalid: -Wsign-conversion is not an option that controls warnings

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68657

--- Comment #11 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Created attachment 38672
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=38672&action=edit
gcc7-pr68657.patch

Untested fix.  With -Werror we even suggest in diagnostic -Werror=psabi, which
doesn't actually work.  That said, this should have been filed as a separate
PR, rather than hijacking an already fixed one.