libstdc++/3174: sparc-rtems (also seen on i386-rtems)

[Joel Sherrill]

Benjamin Kosnik wrote:

> AC_EGREP_HEADER vs AC_TRY_COMPILE. It should sove it.
> 
It didn't.  I still get the same failure on i386 and sparc-rtems. 

Remember the problem is not the version test itself -- it is the fact 
that the
wrong CPP is being used -- the native instead of the cross one.  All other
tests use the cross compiler.

--joel