gh-121404: rearrange code in compile.c so that codegen functions come first and compiler functions second

[iritkatriel]

This PR mostly just moves code around. It places the codegen functions first and the compiler functions after.
The next step will be to move the compiler struct definition after codegen (a bit more tidying up is needed before that).
Also undefine the codegen macros before the compiler code. Then we will know that the two parts are independent, and can split them into two files.

• Issue: split compiler.c into compiler and codegen #121404

[carljm]

This is too much moved code to review the whole diff -- I'm trusting that there aren't substantive changes, just rearrangement, and that tests pass unmodified. (If there are any areas of substantive change that you want looked into more carefully, please point them out!)

[iritkatriel]

This is too much moved code to review the whole diff -- I'm trusting that there aren't substantive changes, just rearrangement, and that tests pass unmodified. (If there are any areas of substantive change that you want looked into more carefully, please point them out!)

Indeed there are no substantial changes in this PR. Thanks.