Implement CST_CODE_CE_GEP (replacing CST_CODE_CE_GEP_OLD in LLVM 19)

[RyanGlScott]

LLVM 19 adds the ability to nusw and nuw flags to constant getelementptr expressions. As a result, there is now a new CST_CODE_CE_GEP (constant code 32), which replaces what is now known as CST_CODE_CE_GEP_OLD (constant code 12). This was implemented on the LLVM side in commit llvm/llvm-project@8cdecd4.

We will need to implement support for this on the llvm-pretty-bc-parser side. A minimal example that currently fails:

%struct.RT = type { i8, [10 x [20 x i32]], i8 }
%struct.ST = type { i32, double, %struct.RT }

@.s = private constant %struct.ST zeroinitializer

define ptr @foo() {
entry:
  ret ptr getelementptr inbounds (%struct.ST, ptr @.s, i64 1, i32 2, i32 1, i64 5, i64 13)
}

If you compile this to bitcode using llvm-as-19.1.0 and attempt to parse the resulting bitcode, it will fail with:

λ> parseBitCodeFromFile "test.bc"
Left (Error {errContext = ["CONSTANTS_BLOCK","@foo","FUNCTION_BLOCK","FUNCTION_BLOCK_ID","value symbol table","MODULE_BLOCK","Bitstream"], errMessage = "Unknown constant record code 32\nAre you sure you're using a supported compiler?\nCheck here: https://github.com/GaloisInc/llvm-pretty-bc-parser\n"})