Global: don't require sysinfo.h globally

... which is Linux specific

src/detection/processes/processes_linux.c

@@ -1,12 +1,11 @@
 #include "processes.h"
 
-uint32_t ffDetectProcesses(FFinstance* instance, FFstrbuf* error)
+#include <sys/sysinfo.h>
+
+uint32_t ffDetectProcesses(FFstrbuf* error)
 {
-    #if FF_HAVE_SYSINFO_H
-        FF_UNUSED(error);
-        return (uint32_t) instance->state.sysinfo.procs;
-    #else
-        ffStrbufAppendS(error, "Unimplemented");
-        return 0;
-    #endif
+    struct sysinfo info;
+    if(sysinfo(&info) != 0)
+        ffStrbufAppendS(error, "sysinfo() failed");
+    return (uint32_t) info.procs;
 }