From upstream master branch:
https://github.com/Itseez/opencv/blob/master/modules/core/src/

Do not include sysctl.h targeting Linux systems.

Signed-off-by: Waldemar Brodkorb <wbx@openadk.org>

diff -Nur opencv-2.4.12.3.orig/modules/core/src/parallel.cpp opencv-2.4.12.3/modules/core/src/parallel.cpp
--- opencv-2.4.12.3.orig/modules/core/src/parallel.cpp	2015-10-26 08:56:34.000000000 +0100
+++ opencv-2.4.12.3/modules/core/src/parallel.cpp	2016-04-05 12:59:37.750143762 +0200
@@ -56,7 +56,7 @@
     #include <sys/types.h>
     #if defined ANDROID
         #include <sys/sysconf.h>
-    #else
+    #elif defined __APPLE__
         #include <sys/sysctl.h>
     #endif
 #endif
diff -Nur opencv-2.4.12.3.orig/modules/core/src/system.cpp opencv-2.4.12.3/modules/core/src/system.cpp
--- opencv-2.4.12.3.orig/modules/core/src/system.cpp	2015-10-26 08:56:34.000000000 +0100
+++ opencv-2.4.12.3/modules/core/src/system.cpp	2016-04-05 13:05:22.468323717 +0200
@@ -163,7 +163,7 @@
 #include <sys/types.h>
 #if defined ANDROID
 #include <sys/sysconf.h>
-#else
+#elif defined __APPLE__
 #include <sys/sysctl.h>
 #endif
 #endif
