feat(asm): add LoongArch encoder with ELF and GOOBJ emission

Assisted-by: DeepSeek V4 Pro

parser/parser.go

@@ -298,10 +298,14 @@ func parseSymbolPrefix(g []token.Token) (*ast.Symbol, int) {
 		sym.Static = true
 		i += 2
 	}
-	if i < len(g) && g[i].Kind == token.Plus {
+	if i < len(g) && (g[i].Kind == token.Plus || g[i].Kind == token.Minus) {
+		neg := g[i].Kind == token.Minus
 		i++
 		if i < len(g) && g[i].Kind == token.Number {
 			sym.Offset, sym.HasOff = parseInt(g[i].Text), true
+			if neg {
+				sym.Offset = -sym.Offset
+			}
 			i++
 		}
 	}