Work around a page size issue on Cygwin.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@72332 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/System/Unix/Process.inc b/lib/System/Unix/Process.inc
index e4f37a1..74b9bb8 100644
--- a/lib/System/Unix/Process.inc
+++ b/lib/System/Unix/Process.inc
@@ -42,7 +42,12 @@
 unsigned 
 Process::GetPageSize() 
 {
-#if defined(HAVE_GETPAGESIZE)
+#if defined(__CYGWIN__)
+  // On Cygwin, getpagesize() returns 64k but the page size for the purposes of
+  // memory protection and mmap() is 4k.
+  // See http://www.cygwin.com/ml/cygwin/2009-01/threads.html#00492
+  static const int page_size = 0x1000;
+#elif defined(HAVE_GETPAGESIZE)
   static const int page_size = ::getpagesize();
 #elif defined(HAVE_SYSCONF)
   static long page_size = ::sysconf(_SC_PAGE_SIZE);