Parser: Add support for missing '=' in designated init

src/aro/Diagnostics.zig

@@ -222,6 +222,7 @@ pub const Options = struct {
     @"address-of-packed-member": Kind = .default,
     nonnull: Kind = .default,
     @"atomic-access": Kind = .default,
+    @"gnu-designator": Kind = .default,
 };
 
 const Diagnostics = @This();

src/aro/Diagnostics/messages.def

@@ -2628,3 +2628,8 @@ attribute_param_out_of_bounds
 alloc_align_required_int_param
     .msg = "'alloc_align' attribute argument may only refer to a function parameter of integer type"
     .kind = .@"error"
+
+gnu_missing_eq_designator
+    .msg = "use of GNU 'missing =' extension in designator"
+    .kind = .warning
+    .opt = W("gnu-designator")

src/aro/Parser.zig

@@ -3890,7 +3890,11 @@ fn initializerItem(p: *Parser, il: *InitList, init_qt: QualType) Error!bool {
         if (designation) index_hint = null;
         defer index_hint = cur_index_hint orelse null;
 
-        if (designation) _ = try p.expectToken(.equal);
+        if (designation) {
+            if (p.eatToken(.equal) == null) {
+                try p.err(.gnu_missing_eq_designator);
+            }
+        }
 
         if (!designation and cur_qt.hasAttribute(p.comp, .designated_init)) {
             try p.err(.designated_init_needed);

test/cases/gnu designated init extension.c

@@ -0,0 +1,6 @@
+int x[] = {[1] 2, [3] 4};
+_Static_assert(sizeof(x) == sizeof(int[4]), "Incorrect array size");
+
+#define EXPECTED_ERRORS "gnu designated init extension.c:1:16: warning: use of GNU 'missing =' extension in designator [-Wgnu-designator]" \
+	"gnu designated init extension.c:1:23: warning: use of GNU 'missing =' extension in designator [-Wgnu-designator]" \
+