build: Check that mlockall() exists

Instead of assuming that all POSIX platforms provide mlockall(),
test for it in configure. If the host doesn't provide this platform
then os_mlock() will fail -ENOSYS, as it does already on Windows.

This is necessary for Haiku, which does not have mlockall().

Signed-off-by: David Carlier <devnexen@gmail.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 20200703145614.16684-4-peter.maydell@linaro.org
[PMM: Expanded commit message; rename to HAVE_MLOCKALL]
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
diff --git a/os-posix.c b/os-posix.c
index 3cd52e1..b674b20 100644
--- a/os-posix.c
+++ b/os-posix.c
@@ -337,6 +337,7 @@
 
 int os_mlock(void)
 {
+#ifdef HAVE_MLOCKALL
     int ret = 0;
 
     ret = mlockall(MCL_CURRENT | MCL_FUTURE);
@@ -345,4 +346,7 @@
     }
 
     return ret;
+#else
+    return -ENOSYS;
+#endif
 }