configure: Make epoll_create1 test work around SPARC glibc bug

configure: Make epoll_create1 test work around SPARC glibc bug

Work around a SPARC glibc bug which caused the epoll_create1 configure
test to wrongly claim that the function was present. Some versions of
SPARC glibc provided the function in the library but didn't declare
it in the include file; the result is that gcc warns about an implicit
declaration but a link succeeds. So we reference the function as a
value rather than a function call to induce a compile time error
if the declaration was not present.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>