Use of statement expression in tblgen generated code

We generate some code in the form of statement expressions in tblgen here:
https://github.com/EnzymeAD/Enzyme/blob/43f2c03825db2dbc46c86f10e46db6867595a1c0/enzyme/tools/enzyme-tblgen/enzyme-tblgen.cpp#L167-L203

Since [statement expression](https://gcc.gnu.org/onlinedocs/gcc/Statement-Exprs.html) is a GNU extension rather than c/c++ standard, and is not supported by MSVC, I am not sure whether we need to replace them via lambda expressions.

cc @ZuseZ4