[Bug bootstrap/78251] config/gettext.m4 and config/iconv.m4 contaminate CPPFLAGS

[mikestump at comcast dot net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78251

--- Comment #3 from Mike Stump <mikestump at comcast dot net> ---
I've been avoiding this bug for years by just removing the unwind.h header. 
:-(