llvm-wrapper: fix warning C4305

llvm-wrapper/ArchiveWrapper.cpp(70): warning C4305: 'argument': truncation from 'int' to 'bool'
while in llvm 12 signature was
 static ErrorOr<std::unique_ptr<MemoryBuffer>> getFile(const Twine &Filename, int64_t FileSize = -1, bool RequiresNullTerminator = true, bool IsVolatile = false);
https://github.com/llvm/llvm-project/blame/fed41342a82f5a3a9201819a82bf7a48313e296b/llvm/include/llvm/Support/MemoryBuffer.h#L85-L87

in llvm 13 and later it was changed to
static ErrorOr<std::unique_ptr<MemoryBuffer>> getFile(const Twine &Filename, bool IsText = false, bool RequiresNullTerminator = true, bool IsVolatile = false);
https://github.com/llvm/llvm-project/blame/75e33f71c2dae584b13a7d1186ae0a038ba98838/llvm/include/llvm/Support/MemoryBuffer.h#L86-L88

so code was interpreted as MemoryBuffer::getFile(Path, /*IsText*/true, /*RequiresNullTerminator=*/false), but now will be MemoryBuffer::getFile(Path, /*IsText*/false, /*RequiresNullTerminator=*/false). How that worked before?

compiler/rustc_llvm/llvm-wrapper/ArchiveWrapper.cpp

@@ -67,7 +67,7 @@ typedef RustArchiveIterator *LLVMRustArchiveIteratorRef;
 
 extern "C" LLVMRustArchiveRef LLVMRustOpenArchive(char *Path) {
   ErrorOr<std::unique_ptr<MemoryBuffer>> BufOr =
-      MemoryBuffer::getFile(Path, -1, false);
+      MemoryBuffer::getFile(Path, /*IsText*/false, /*RequiresNullTerminator=*/false);
   if (!BufOr) {
     LLVMRustSetLastError(BufOr.getError().message().c_str());
     return nullptr;