Core: Sidestep GCC false-positives

(cherry picked from commit acdb8667b5)

Adds some more fixes for 4.5 and earlier.

Co-authored-by: Rémi Verschelde <rverschelde@gmail.com>

core/io/image.cpp

@@ -2331,6 +2331,10 @@ void Image::initialize_data(const char **p_xpm) {
 			} break;
 			case READING_PIXELS: {
 				int y = line - colormap_size - 1;
+#if defined(__GNUC__) && !defined(__clang__)
+#pragma GCC diagnostic push
+#pragma GCC diagnostic warning "-Wstringop-overflow=0"
+#endif
 				for (int x = 0; x < size_width; x++) {
 					char pixelstr[6] = { 0, 0, 0, 0, 0, 0 };
 					for (int i = 0; i < pixelchars; i++) {
@@ -2345,6 +2349,9 @@ void Image::initialize_data(const char **p_xpm) {
 					}
 					_put_pixelb(x, y, pixel_size, data_write, pixel);
 				}
+#if defined(__GNUC__) && !defined(__clang__)
+#pragma GCC diagnostic pop
+#endif
 
 				if (y == (size_height - 1)) {
 					status = DONE;

core/math/geometry_2d.cpp

@@ -30,7 +30,14 @@
 
 #include "geometry_2d.h"
 
+#if defined(__GNUC__) && !defined(__clang__)
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Walloc-zero"
+#endif
 #include "thirdparty/clipper2/include/clipper2/clipper.h"
+#if defined(__GNUC__) && !defined(__clang__)
+#pragma GCC diagnostic pop
+#endif
 #include "thirdparty/misc/polypartition.h"
 #define STB_RECT_PACK_IMPLEMENTATION
 #include "thirdparty/misc/stb_rect_pack.h"

scene/resources/packed_scene.cpp

@@ -158,6 +158,7 @@ Node *SceneState::instantiate(GenEditState p_edit_state) const {
 	const NodeData *nd = &nodes[0];
 
 	Node **ret_nodes = (Node **)alloca(sizeof(Node *) * nc);
+	ret_nodes[0] = nullptr; // Sidesteps "maybe uninitialized" false-positives on GCC.
 
 	bool gen_node_path_cache = p_edit_state != GEN_EDIT_STATE_DISABLED && node_path_cache.is_empty();