[Object][Wasm] Allow parsing of GC types in type and table sections (#79235)

This change allows a WasmObjectFile to be created from a wasm file even 
if it uses typed funcrefs and GC types. It does not significantly change how 
lib/Object models its various internal types (e.g. WasmSignature,
WasmElemSegment), so LLVM does not really "support" or understand such
files, but it is sufficient to parse the type, global and element sections, discarding
types that are not understood. This is useful for low-level binary tools such as
nm and objcopy, which use only limited aspects of the binary (such as function
definitions) or deal with sections as opaque blobs.

This is done by allowing `WasmValType` to have a value of `OTHERREF`
(representing any unmodeled reference type), and adding a field to
`WasmSignature` indicating it's a placeholder for an unmodeled reference 
type (since there is a 1:1 correspondence between WasmSignature objects
and types in the type section).
Then the object file parsers for the type and element sections are expanded
to parse encoded reference types and discard any unmodeled fields.

1 files changed, 2 insertions, 1 deletions

diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp
index 908efbb..fb949d4 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp
@@ -125,8 +125,9 @@ static char getInvokeSig(wasm::ValType VT) {
     return 'F';
   case wasm::ValType::EXTERNREF:
     return 'X';
+  default:
+    llvm_unreachable("Unhandled wasm::ValType enum");
   }
-  llvm_unreachable("Unhandled wasm::ValType enum");
 }
 
 // Given the wasm signature, generate the invoke name in the format JS glue code