[llvm] [llvm] DLLExport BinaryStreamReader (PR #127910)

[Andrew Rogers via llvm-commits]

https://github.com/andrurogerz created https://github.com/llvm/llvm-project/pull/127910

## Overview
Annotate the `llvm::BinaryStreamReader` class so it is explicitly included in LLVM's public interface. When building LLVM as a Windows DLL, this annotation exports `BinaryStreamReader`'s public methods from the DLL.

## Background
This change is required as part of the overall project to build LLVM as a Windows DLL described in #109483. Without this change, LLVM tools fail to link.

## Validation
Built LLVM with MSVC on Windows 11:
```
cmake -B build -S llvm -G Ninja -DCMAKE_BUILD_TYPE=Debug -DLLVM_ENABLE_PROJECTS="clang" -DLLVM_OPTIMIZED_TABLEGEN -DLLVM_BUILD_LLVM_DYLIB=ON -DLLVM_BUILD_LLVM_DYLIB_VIS=ON -DLLVM_LINK_LLVM_DYLIB=ON -DCLANG_LINK_CLANG_DYLIB=ON
ninja -C build llvm-rc llvm-ar
```
Verified the annotated interface no longer appears in the list of unresolved external symbols.

>From 7b7cdac32bf6a27be6c1dadb1a4e8f03bacb1472 Mon Sep 17 00:00:00 2001
From: Andrew Rogers <andrurogerz at gmail.com>
Date: Wed, 19 Feb 2025 13:07:19 -0800
Subject: [PATCH] DLLExport BinaryStreamReader

---
 llvm/include/llvm/Support/BinaryStreamReader.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/llvm/include/llvm/Support/BinaryStreamReader.h b/llvm/include/llvm/Support/BinaryStreamReader.h
index ca99388c5d03a..e61349d841cdb 100644
--- a/llvm/include/llvm/Support/BinaryStreamReader.h
+++ b/llvm/include/llvm/Support/BinaryStreamReader.h
@@ -14,6 +14,7 @@
 #include "llvm/Support/Alignment.h"
 #include "llvm/Support/BinaryStreamArray.h"
 #include "llvm/Support/BinaryStreamRef.h"
+#include "llvm/Support/Compiler.h"
 #include "llvm/Support/ConvertUTF.h"
 #include "llvm/Support/Endian.h"
 #include "llvm/Support/Error.h"
@@ -26,7 +27,7 @@ namespace llvm {
 /// null-terminated strings, integers in various flavors of endianness, etc.
 /// Can be subclassed to provide reading of custom datatypes, although no
 /// are overridable.
-class BinaryStreamReader {
+class LLVM_ABI BinaryStreamReader {
 public:
   BinaryStreamReader() = default;
   explicit BinaryStreamReader(BinaryStreamRef Ref);