I had been looking at the wrong line all along when attempting to fix:
```
core/os/memory.cpp:184:13: warning: unused variable 's' [-Wunused-variable]
uint64_t *s = (uint64_t *)mem;
^
```
the tile cursor did not follow the mouse cursor, and the tile grid was displayed wrong,
because the forward_canvas_draw_over_viewport function used the wrong xform and thus its
map_to_world is not the inverse of the mouse interactor world_to_map, making the tiles
draw from 0,0 of the screen instead of 0,0 of the tile map (which is in a different place)
Fixes the following GCC 8 warnings:
```
core/image.cpp:730:44: warning: 'mip1_weight' may be used uninitialized in this function [-Wmaybe-uninitialized]
core/image.cpp:293:20: warning: 'mip2' may be used uninitialized in this function [-Wmaybe-uninitialized]
core/image.cpp:293:20: warning: 'mip1' may be used uninitialized in this function [-Wmaybe-uninitialized]
editor/audio_stream_preview.cpp:58:19: warning: 'vmax' may be used uninitialized in this function [-Wmaybe-uninitialized]
editor/audio_stream_preview.cpp:85:19: warning: 'vmin' may be used uninitialized in this function [-Wmaybe-uninitialized]
editor/editor_themes.cpp:306:53: warning: 'preset_contrast' may be used uninitialized in this function [-Wmaybe-uninitialized]
editor/plugins/animation_blend_space_2d_editor.cpp:459:27: warning: 'prev_idx' may be used uninitialized in this function [-Wmaybe-uninitialized]
editor/plugins/animation_blend_space_2d_editor.cpp:443:27: warning: 'prev_idx' may be used uninitialized in this function [-Wmaybe-uninitialized]
main/tests/test_oa_hash_map.cpp:57:29: warning: 'value' may be used uninitialized in this function [-Wmaybe-uninitialized]
modules/csg/csg.cpp:764:40: warning: 'max_angle' may be used uninitialized in this function [-Wmaybe-uninitialized]
modules/csg/csg_shape.cpp:1945:3: warning: 'face_count' may be used uninitialized in this function [-Wmaybe-uninitialized]
scene/3d/voxel_light_baker.cpp:1593:8: warning: 'cone_aperture' may be used uninitialized in this function [-Wmaybe-uninitialized]
scene/3d/voxel_light_baker.cpp:1592:6: warning: 'cone_dir_count' may be used uninitialized in this function [-Wmaybe-uninitialized]
scene/animation/animation_blend_space_2d.cpp:471:8: warning: 'mind' may be used uninitialized in this function [-Wmaybe-uninitialized]
core/os/memory.cpp:94: warning: ignoring #pragma clang diagnostic [-Wunknown-pragmas]
core/os/memory.cpp:95: warning: ignoring #pragma clang diagnostic [-Wunknown-pragmas]
core/os/memory.cpp:98: warning: ignoring #pragma clang diagnostic [-Wunknown-pragmas]
```
Fixes the following GCC/Clang warnings:
```
modules/gdnative/nativescript/nativescript.h:280:37: warning: non-static data member initializers only available with -std=c++11 or -std=gnu++11
modules/gdnative/nativescript/nativescript.h:281:37: warning: non-static data member initializers only available with -std=c++11 or -std=gnu++11
modules/gdnative/nativescript/nativescript.h:283:42: warning: non-static data member initializers only available with -std=c++11 or -std=gnu++11
modules/gdnative/nativescript/nativescript.h:285:38: warning: non-static data member initializers only available with -std=c++11 or -std=gnu++11
modules/gdnative/nativescript/nativescript.h:287:38: warning: non-static data member initializers only available with -std=c++11 or -std=gnu++11
modules/gdnative/nativescript/nativescript.h:290:45: warning: non-static data member initializers only available with -std=c++11 or -std=gnu++11
modules/gdnative/nativescript/nativescript.h:291:44: warning: non-static data member initializers only available with -std=c++11 or -std=gnu++11
```
