cmake: Disable warnings for most externals on MSVC, like we do in the VS project files.

Externals/curl/lib/CMakeLists.txt

@@ -12,6 +12,7 @@ add_library(
   STATIC
   ${SRCS}
   )
+dolphin_disable_warnings_msvc(curl)
 
 target_link_libraries(curl ${MBEDTLS_LIBRARIES} z)
 target_compile_definitions(curl PUBLIC CURL_STATICLIB PRIVATE CURL_DISABLE_LDAP)