Automation of reverse operations C ++ 11 auto-communications

Question

I have a C ++ 11 code base that I need to build using the pre-11 toolchain. Most of the 11 features used have enhancement equivalents, so this is not a big deal. But there are a lot of auto declarations. Is there a good source code preprocessing method to replace all auto-declarations with an explicit type? Perhaps redefine auto as MYUNKNOWNTYPE, then run each file through the compiler and parse "cannot convert the_type_i_actually_wanted to MYUNKNOWNTYPE", or maybe there is some trace / diag option in gcc / clang version 11 that will throw them all out? Thanks.