No mincore(2) on OpenBSD.

Index: Source/JavaScriptCore/heap/BlockDirectory.cpp
--- Source/JavaScriptCore/heap/BlockDirectory.cpp.orig
+++ Source/JavaScriptCore/heap/BlockDirectory.cpp
@@ -69,7 +69,7 @@ void BlockDirectory::updatePercentageOfPagedOutPages(S
     // FIXME: We should figure out a solution for Windows and PlayStation.
     // QNX doesn't have mincore(), though the information can be had. But since all mapped
     // pages are resident, does it matter?
-#if OS(UNIX) && !PLATFORM(PLAYSTATION) && !OS(QNX) && !OS(HAIKU)
+#if OS(UNIX) && !PLATFORM(PLAYSTATION) && !OS(QNX) && !OS(HAIKU) && !OS(OPENBSD)
     size_t pageSize = WTF::pageSize();
     ASSERT(!(MarkedBlock::blockSize % pageSize));
     auto numberOfPagesInMarkedBlock = MarkedBlock::blockSize / pageSize;
