What's this AC_TRY_RUN thingie?

[juergen quotus com (Juergen Fiedler)]

Hi, 

I' think I'm making some progress in compiling Gnome, but there are still some
things that remain a mystery to me. Like this AC_TRY_RUN warning. I was
compiling glib and autogen.sh gave me dozens of errors that looked like this:

configure.in:216: warning: AC_TRY_RUN called without default to allow cross
compiling

(only with varying line numbers). Glib compiles quite fine afterwards, but it's
puzzling me. I'd rather get rid of all (or at least most) warnings.
Could someone please tell me how to deal with this particular one?

TIA,
Juergen