Build gcc with C++ support fails when can't find libc headers

[Fiodar Stryzhniou via gcc-help]

Hi! When I build gcc and libc headers should not be aviable at configure stage. Libsupc++' configure fails and aborts compiler building. I need libsupc++ only.
 After some research I find 2 cause:
1) <include > which not used in base type size checks
2) abort if time.h not found
I change configure script with sed and got working compiler. Why are that checks used?
You can look at my build script here - https://github.com/fedor4ever/GCC-4-Symbian
Fiodar Stryzhniou