Should build-sysroot be considered for setting inhibit_libc?

[Stephen M. Kenton]

I'm working on a patch to the top level configure to detect if inhibit_libc
will set for gcc and to avoid trying to build certain libraries in that 
case.
I started to just clone the inhibit_libc logic from the gcc/configure, 
but as
Ian commented, it is a bit strange.  Then I realized that build-sysroot 
is not
checked at all.  Under what conditions should inhibit_libc really be set?
Extending the current logic would result in this, is it what is really 
wanted?

1. Cross compiling with no build-sysroot, sysroot, or headers specified

2. Newlib is explicitly specified regardless of build-sysroot or sysroot
    but without headers specified.

Should specifiying newlib in the absence of the newlib source continue
to be treated as meaning "force inhibit_libc" in some cases, or should
inhibit_libc just be exposed if that is desirable?

Steve Kenton