Squashed 'third_party/eigen/' changes from 61d72f6..cf794d3


Change-Id: I9b814151b01f49af6337a8605d0c42a3a1ed4c72
git-subtree-dir: third_party/eigen
git-subtree-split: cf794d3b741a6278df169e58461f8529f43bce5d
diff --git a/cmake/EigenDetermineOSVersion.cmake b/cmake/EigenDetermineOSVersion.cmake
index 3c48d4c..9246fa6 100644
--- a/cmake/EigenDetermineOSVersion.cmake
+++ b/cmake/EigenDetermineOSVersion.cmake
@@ -26,7 +26,7 @@
 endfunction()
 
 function(DetermineOSVersion OS_VERSION)
-  if (WIN32)
+  if (WIN32 AND CMAKE_HOST_SYSTEM_NAME MATCHES Windows)
     file (TO_NATIVE_PATH "$ENV{COMSPEC}" SHELL)
     exec_program( ${SHELL} ARGS "/c" "ver" OUTPUT_VARIABLE ver_output)