getrandom: Override incompatible system function on Solaris 11.
* lib/sys_random.in.h (getrandom): Override if REPLACE_GETRANDOM is 1.
* lib/getrandom.c (getrandom): When the system has getrandom, just
invoke it.
* m4/getrandom.m4 (gl_FUNC_GETRANDOM): Set REPLACE_GETRANDOM if the
system's getrandom function's prototype is not the expected one.
* m4/sys_random_h.m4 (gl_SYS_RANDOM_H_DEFAULTS): Initialize
REPLACE_GETRANDOM.
* modules/sys_random (Makefile.am): Substitute REPLACE_GETRANDOM.
* modules/getrandom (modules/getrandom): Consider REPLACE_GETRANDOM.
* tests/test-getrandom.c (main): Allow error EINVAL as an alternative to
EAGAIN.
* doc/glibc-functions/getrandom.texi: Mention the new module and the
Solaris problem.