[WebAssembly][lld] Fix crash when applying relocations to debug sections

Debug sections are special in that they can contain relocations against
symbols that are not present in the final output (i.e. not live).
However it is also possible to have R_WASM_TABLE_INDEX relocations
against symbols that don't have a table index assigned (since they are
not address taken by actual code.

Fixes: emscripten-core/emscripten#9023

Differential Revision: https://reviews.llvm.org/D66435

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@369423 91177308-0d34-0410-b5e6-96231b3b80d8

lib/MC/MCParser/WasmAsmParser.cpp

@@ -123,6 +123,7 @@ class WasmAsmParser : public MCAsmParserExtension {
                     // See use of .init_array in WasmObjectWriter and
                     // TargetLoweringObjectFileWasm
                     .StartsWith(".init_array", SectionKind::getData())
+                    .StartsWith(".debug_", SectionKind::getMetadata())
                     .Default(Optional<SectionKind>());
     if (!Kind.hasValue())
       return Parser->Error(Lexer->getLoc(), "unknown section kind: " + Name);