Fix ByVal args handling

[frabert]

Fixes #195

[pgoodman]

@frabert Are any of the things in tyat build_linux for ubuntu 20.04 on llvm-12 issues?

[frabert]

The issue seems to be about dangling references or something like that...

Use still stuck around after Def is destroyed:  <badref> = load i32, i32* @SDVO_CMD_GET_MAX_OVERSCAN_H, align 4, !dbg !DILocation(line: 74, column: 8, scope: <0x4f579c0>), !tbaa <0x4f5a598>
rellic-decomp-12.0: /__w/cxx-common/cxx-common/vcpkg/buildtrees/llvm-12/src/org-12.0.1-5ce32a7629.clean/llvm/lib/IR/Value.cpp:100: llvm::Value::~Value(): Assertion `materialized_use_empty() && "Uses remain when a value is destroyed!"' failed.```