Try disabling warning 4191.

Author: jonsimantov

cmake/external_rules.cmake

@@ -188,6 +188,8 @@ function(build_external_dependencies)
       set(CMAKE_SUB_BUILD_OPTIONS ${CMAKE_SUB_BUILD_OPTIONS}
           --config Release)
     endif()
+    # On Windows, disable warning 4191: unsafe type conversion
+    set(disable_warnings "/WD4191")
     if(MSVC_RUNTIME_LIBRARY_STATIC)
       set(CMAKE_SUB_CONFIGURE_OPTIONS ${CMAKE_SUB_CONFIGURE_OPTIONS}
           -DCMAKE_C_FLAGS_RELEASE="/MT"
@@ -196,13 +198,13 @@ function(build_external_dependencies)
           -DCMAKE_CXX_FLAGS_DEBUG="/MTd")
       if (CMAKE_BUILD_TYPE STREQUAL "Debug")
         set(CMAKE_SUB_CONFIGURE_OPTIONS ${CMAKE_SUB_CONFIGURE_OPTIONS}
-            -DCMAKE_C_FLAGS="/MTd"
-            -DCMAKE_CXX_FLAGS="/MTd"
+            -DCMAKE_C_FLAGS="/MTd ${disable_warnings}"
+            -DCMAKE_CXX_FLAGS="/MTd ${disable_warnings}"
             -DCMAKE_MSVC_RUNTIME_LIBRARY=MultiThreadedDebug)
       else()
         set(CMAKE_SUB_CONFIGURE_OPTIONS ${CMAKE_SUB_CONFIGURE_OPTIONS}
-            -DCMAKE_C_FLAGS="/MT"
-            -DCMAKE_CXX_FLAGS="/MT"
+            -DCMAKE_C_FLAGS="/MT ${disable_warnings}"
+            -DCMAKE_CXX_FLAGS="/MT ${disable_warnings}"
             -DCMAKE_MSVC_RUNTIME_LIBRARY=MultiThreaded)
       endif()
     else()  # dynamic (DLL) runtime
@@ -213,13 +215,13 @@ function(build_external_dependencies)
           -DCMAKE_CXX_FLAGS_DEBUG="/MDd")
       if (CMAKE_BUILD_TYPE STREQUAL "Debug")
         set(CMAKE_SUB_CONFIGURE_OPTIONS ${CMAKE_SUB_CONFIGURE_OPTIONS}
-            -DCMAKE_C_FLAGS="/MDd"
-            -DCMAKE_CXX_FLAGS="/MDd"
+            -DCMAKE_C_FLAGS="/MDd ${disable_warnings}"
+            -DCMAKE_CXX_FLAGS="/MDd ${disable_warnings}"
             -DCMAKE_MSVC_RUNTIME_LIBRARY=MultiThreadedDebugDLL)
       else()
         set(CMAKE_SUB_CONFIGURE_OPTIONS ${CMAKE_SUB_CONFIGURE_OPTIONS}
-            -DCMAKE_C_FLAGS="/MD"
-            -DCMAKE_CXX_FLAGS="/MD"
+            -DCMAKE_C_FLAGS="/MD ${disable_warnings}"
+            -DCMAKE_CXX_FLAGS="/MD ${disable_warnings}"
             -DCMAKE_MSVC_RUNTIME_LIBRARY=MultiThreadedDLL)
       endif()
     endif()