[clang] [clang][bytecode] Fix a diagnostic discrepancy (PR #177384)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Timm Baeder (tbaederr)

<details>
<summary>Changes</summary>

The current interpreter does _not_ evaluate function calls when checking for a potential constant expression.

However, it _does_ evaluate the initializers of constructors. In the bytecode interpreter, this is harder because we compile the initializers and the body of a constructor all in the same function. 

Add a special opcode that we emit after the constructor initializers and that aborts when we're checking for a potential constant expression.

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Full diff: https://github.com/llvm/llvm-project/pull/177384.diff


5 Files Affected:

- (modified) clang/lib/AST/ByteCode/Compiler.cpp (+6-1) 
- (modified) clang/lib/AST/ByteCode/Interp.cpp (+5-6) 
- (modified) clang/lib/AST/ByteCode/Interp.h (+10) 
- (modified) clang/lib/AST/ByteCode/Opcodes.td (+2) 
- (modified) clang/test/AST/ByteCode/functions.cpp (+24) 


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</details>


https://github.com/llvm/llvm-project/pull/177384