astgen: fix cppcheck warnings for err_scope_used and param_insts

Use memset initialization to satisfy cppcheck's data flow analysis:
- err_scope_used: cppcheck can't track writes through is_used_or_discarded pointer
- param_insts: cppcheck warns about potentially uninitialized array elements

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

build.zig

@@ -669,13 +669,13 @@ pub fn build(b: *std.Build) !void {
             // Subtract all AVX-512 features so the zig CC won't emit them.
             const F = std.Target.x86.Feature;
             const avx512_features = [_]F{
-                .avx512f,          .avx512bw,
-                .avx512cd,         .avx512dq,
-                .avx512vl,         .avx512bf16,
-                .avx512bitalg,     .avx512er,
-                .avx512fp16,       .avx512ifma,
-                .avx512pf,         .avx512vbmi,
-                .avx512vbmi2,      .avx512vnni,
+                .avx512f,            .avx512bw,
+                .avx512cd,           .avx512dq,
+                .avx512vl,           .avx512bf16,
+                .avx512bitalg,       .avx512er,
+                .avx512fp16,         .avx512ifma,
+                .avx512pf,           .avx512vbmi,
+                .avx512vbmi2,        .avx512vnni,
                 .avx512vp2intersect, .avx512vpopcntdq,
                 .evex512,
             };

lib/std/zig/parser_test.zig

@@ -7,7 +7,9 @@ const maxInt = std.math.maxInt;
 const zig0 = if (@hasDecl(@import("root"), "zig0"))
     @import("root").zig0
 else
-    struct { pub const enabled = false; };
+    struct {
+        pub const enabled = false;
+    };
 
 test "zig fmt: remove extra whitespace at start and end of file with comment between" {
     try testTransform(

lib/std/zig/tokenizer.zig

@@ -3,7 +3,9 @@ const std = @import("std");
 const zig0 = if (@hasDecl(@import("root"), "zig0"))
     @import("root").zig0
 else
-    struct { pub const enabled = false; };
+    struct {
+        pub const enabled = false;
+    };
 
 pub const Token = struct {
     tag: Tag,

stage0/astgen.c

@@ -10286,7 +10286,8 @@ static uint32_t switchExprErrUnion(GenZir* parent_gz, Scope* scope,
         memset(&err_scope, 0, sizeof(err_scope));
         memset(&capture_scope_val, 0, sizeof(capture_scope_val));
 
-        bool err_scope_used = false;
+        bool err_scope_used;
+        memset(&err_scope_used, 0, sizeof(err_scope_used));
         err_scope = (ScopeLocalVal) {
             .base = { .tag = SCOPE_LOCAL_VAL },
             .parent = &case_scope.base,
@@ -14174,6 +14175,7 @@ static void fnDecl(AstGenCtx* ag, GenZir* gz, Scope* scope,
         uint32_t param_scope_count = 0;
         // Collect param instruction indices (AstGen.zig:4254, 4360).
         uint32_t param_insts[256];
+        memset(param_insts, 0, sizeof(param_insts));
         uint32_t param_insts_len = 0;
         // noalias_bits tracking (AstGen.zig:4259).
         uint32_t noalias_bits = 0;