astgen: fix while loop dbg_node, block expr rvalue, int_type data issue

- whileExpr: emit emitDbgNode before condition evaluation to match
  upstream AstGen.zig:6579. Fixes astgen_test.zig corpus (1 missing
  DBG_STMT).
- Block expressions in exprRl: wrap blockExprExpr result with rvalue()
  to handle result location storage (RL_PTR → STORE_NODE, etc.).
  Fixes parser_test.zig inst_len to exact match.
- parser_test.zig corpus now has matching inst_len and all tags, but
  has 1 int_type data signedness mismatch (pre-existing issue).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

astgen.c

@@ -4374,7 +4374,7 @@ static uint32_t exprRl(GenZir* gz, Scope* scope, ResultLoc rl, uint32_t node) {
     case AST_NODE_BLOCK_TWO_SEMICOLON:
     case AST_NODE_BLOCK:
     case AST_NODE_BLOCK_SEMICOLON:
-        return blockExprExpr(gz, scope, rl, node);
+        return rvalue(gz, rl, blockExprExpr(gz, scope, rl, node), node);
     // Anonymous array init (AstGen.zig:1119-1127).
     case AST_NODE_ARRAY_INIT_DOT_TWO:
     case AST_NODE_ARRAY_INIT_DOT_TWO_COMMA:
@@ -5611,6 +5611,8 @@ static uint32_t whileExpr(
 
     // Evaluate condition in cond_scope (AstGen.zig:6571-6607).
     GenZir cond_scope = makeSubBlock(&loop_scope, &loop_scope.base);
+    // Emit debug node for the condition expression (AstGen.zig:6579).
+    emitDbgNode(&cond_scope, cond_node);
     uint32_t cond = expr(&cond_scope, &cond_scope.base, cond_node);
 
     // Create condbr + cond_block (AstGen.zig:6609-6615).

astgen_test.zig

@@ -798,8 +798,8 @@ test "astgen: corpus tokenizer_test.zig" {
 }
 
 test "astgen: corpus parser_test.zig" {
-    // TODO: 1 inst diff — 1 STORE_NODE inside ptr-based struct init with
-    // block field init expression.
+    // TODO: int_type signedness data mismatch at inst[6899] — all tags and
+    // inst_len match, but one int_type has ref=signed got=unsigned.
     if (true) return error.SkipZigTest;
     const gpa = std.testing.allocator;
     try corpusCheck(gpa, @embedFile("parser_test.zig"));