[Bug bootstrap/56703] problems with strsignal and maybe strstr due to varying const on return type

[jay.krell at cornell dot edu]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56703

--- Comment #1 from Jay <jay.krell at cornell dot edu> 2013-03-23 23:12:03 UTC ---
I see that the check for any function involves a cast of its type -- i.e. it
isn't customized per-function, so a change isn't trivial.

For now I have removed strstr and strsignal from system.h -- assume they are
declared.