S390: Use compile-only instead of also link-tests in configure.

Some of the s390-specific configure checks are using compile and
link configure tests.  Now use only compile tests as the link
tests fails when e.g. bootstrapping a cross-toolchain due to
missing crt-files/libc.so.  This is achieved by using
AC_COMPILE_IFELSE in configure.ac file.

This is observable e.g. when using buildroot which builds glibc
only once or the build-many-glibcs.py script.  Note that the latter
one is building glibc twice in the compilers-step (configure-checks
fails) and in the glibcs-step (configure-checks succeed).

Note, that the s390 specific configure tests for static PIE have to
link an executable to test binutils support.  Thus we can't fix
those tests.