cgen: fix nested struct generation for globals for gcc (#16614)

vlib/v/checker/tests/globals_run/global_nested_struct_test.vv

@@ -0,0 +1,21 @@
+pub struct Foo {
+    val Bar
+}
+
+pub struct Bar {
+    number int
+}
+
+fn test_get() {
+    
+}
+
+[cinit]
+__global (
+    baz = Foo{Bar{number: 5}}
+)
+
+
+fn main() {
+    print(baz)
+}

vlib/v/gen/c/cgen.v

@@ -140,6 +140,7 @@ mut:
 	inside_const_opt_or_res   bool
 	inside_lambda             bool
 	inside_for_in_any_cond    bool
+	inside_cinit              bool
 	loop_depth                int
 	ternary_names             map[string]string
 	ternary_level_names       map[string][]string
@@ -5050,6 +5051,10 @@ fn (mut g Gen) global_decl(node ast.GlobalDecl) {
 	}
 	// should the global be initialized now, not later in `vinit()`
 	cinit := node.attrs.contains('cinit')
+	g.inside_cinit = cinit
+	defer {
+		g.inside_cinit = false
+	}
 	cextern := node.attrs.contains('c_extern')
 	should_init := (!g.pref.use_cache && g.pref.build_mode != .build_module)
 		|| (g.pref.build_mode == .build_module && g.module_built == node.mod)

vlib/v/gen/c/struct.v

@@ -42,7 +42,8 @@ fn (mut g Gen) struct_init(node ast.StructInit) {
 
 		is_anon = info.is_anon
 	}
-	if !is_anon {
+
+	if !g.inside_cinit && !is_anon {
 		g.write('(')
 		defer {
 			g.write(')')
@@ -63,6 +64,12 @@ fn (mut g Gen) struct_init(node ast.StructInit) {
 		} else {
 			g.write('&(${basetyp}){')
 		}
+	} else if g.inside_cinit {
+		if is_multiline {
+			g.writeln('{')
+		} else {
+			g.write('{')
+		}
 	} else {
 		if is_multiline {
 			g.writeln('(${styp}){')