fix compiler flags for msvc in portable lib (pytorch#15185)

### Test plan
manual for now. When I get a stable config working on msvc I will add ci

Author: JacobSzwejbka

kernels/portable/CMakeLists.txt

@@ -21,7 +21,10 @@ if(NOT EXECUTORCH_ROOT)
   set(EXECUTORCH_ROOT ${CMAKE_CURRENT_SOURCE_DIR}/../..)
 endif()
 
-set(_common_compile_options -Wno-deprecated-declarations)
+set(_common_compile_options
+    $<$<CXX_COMPILER_ID:MSVC>:/wd4996>
+    $<$<NOT:$<CXX_COMPILER_ID:MSVC>>:-Wno-deprecated-declarations>
+)
 
 include(${EXECUTORCH_ROOT}/tools/cmake/Utils.cmake)
 include(${EXECUTORCH_ROOT}/tools/cmake/Codegen.cmake)