Fix up configure to handle architectures that do not implement perf_event_open
This patch fixes the following problems:
1) The configure script allows the user to pass a location to kernel
headers (via --with-kernel option) such that, even if the running
kernel does not have perf_events support, it may be possible to
build operf (e.g., in cross-compile environments). But the message
'This kernel does not have perf_events support; falling back to legacy
oprofile' was being displayed inappropriately in such cases. This
patch changes the configure script so that the "falling back to
legacy oprofile" message will only be displayed if we're running
on a kernel that does not have perf_events support AND the user
did not pass specify the "--with-kernel" option.
2) Some architectures don't even implement the perf_event_open syscall, so the
configure script must do more than checking kernel version and whether or not
perf_event.h is present in order to decide if perf_events is supported.
This patch provides that extra capability.
These problems were reported by Tony Jones <email@example.com>.
Signed-off-by: Maynard Johnson <firstname.lastname@example.org>