Use /Os for x86 build on Windows

Author: BewareMyPower

LegacyFindPackages.cmake

@@ -270,6 +270,11 @@ if (MSVC)
         string(REGEX REPLACE "/MD" "/MT" CMAKE_CXX_FLAGS_DEBUG ${CMAKE_CXX_FLAGS_DEBUG})
         string(REGEX REPLACE "/MD" "/MT" CMAKE_CXX_FLAGS_RELEASE ${CMAKE_CXX_FLAGS_RELEASE})
         string(REGEX REPLACE "/MD" "/MT" CMAKE_CXX_FLAGS_RELWITHDEBINFO ${CMAKE_CXX_FLAGS_RELWITHDEBINFO})
+        if (NOT CMAKE_CL_64)
+            # When building with a 32-bit cl.exe, the virtual address space is limited to 2GB, which could be
+            # reached with /O2 optimization. Use /Os for smaller code size.
+            string(REGEX REPLACE "/O2" "/Os" CMAKE_CXX_FLAGS_RELEASE ${CMAKE_CXX_FLAGS_RELEASE})
+        endif ()
         message(STATUS "CMAKE_CXX_FLAGS_DEBUG: " ${CMAKE_CXX_FLAGS_DEBUG})
         message(STATUS "CMAKE_CXX_FLAGS_RELEASE: " ${CMAKE_CXX_FLAGS_RELEASE})
         message(STATUS "CMAKE_CXX_FLAGS_RELWITHDEBINFO: " ${CMAKE_CXX_FLAGS_RELWITHDEBINFO})