If sys/signalfd.h does not exist, assume that it does not exist
in glibc, rather than that it exists without a corresponding
header file.  Note that this version of the signalfd() wrapper
function (unlike the version in glibc) falls back dynamically to
the old signalfd system call if the signalfd4 system call is not
implemented in the currently-running kernel; the version in glibc
chooses the version of the signalfd system call to make via static
build-time configuration.
Signed-off-by: Michael K Johnson <johnsonm@rpath.com>
Signed-off-by: Daniel Lezcnao <dlezcano@fr.ibm.com>