[build] compilation warnings

[Lecrapouille]

Issue description

Compilation warnings that could be fixed.

Environment

emscripten, Debian 11.
But can be reproduced with extra compilation flags: -Wunused-but-set-variable -Wunused-function -Wimplicit-const-int-float-conversion

Code Example

 In file included from rcore.c:101:
./rlgl.h:3025:9: warning: variable 'mipOffset' set but not used [-Wunused-but-set-variable]
 3025 |     int mipOffset = 0;          // Mipmap data offset, only used for tracelog
      |         ^
In file included from rcore.c:489:
./platforms/rcore_web.c:1006:13: warning: unused function 'WindowMaximizeCallback' [-Wunused-function]
 1006 | static void WindowMaximizeCallback(GLFWwindow *window, int maximized)
      |             ^~~~~~~~~~~~~~~~~~~~~~
./platforms/rcore_web.c:1178:16: warning: unused function 'EmscriptenWindowResizedCallback' [-Wunused-function]
 1178 | static EM_BOOL EmscriptenWindowResizedCallback(int eventType, const EmscriptenUiEvent *event, void *userData)
      |                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
emcc -c rtextures.c -Wall -D_GNU_SOURCE -DPLATFORM_WEB -DGRAPHICS_API_OPENGL_ES2 -Wno-missing-braces -Werror=pointer-arith -fno-strict-aliasing  -std=gnu99 -fPIC -Os -I.  -Iexternal/glfw/include -Iexternal/glfw/deps/mingw
In file included from rtextures.c:216:
./external/stb_image_resize2.h:2866:14: warning: unused function 'stbir__support_zero' [-Wunused-function]
 2866 | static float stbir__support_zero(float s, void * user_data)
      |              ^~~~~~~~~~~~~~~~~~~
3 warnings generated.
emcc -c rtext.c -Wall -D_GNU_SOURCE -DPLATFORM_WEB -DGRAPHICS_API_OPENGL_ES2 -Wno-missing-braces -Werror=pointer-arith -fno-strict-aliasing  -std=gnu99 -fPIC -Os -I.  -Iexternal/glfw/include -Iexternal/glfw/deps/mingw
emcc -c utils.c -Wall -D_GNU_SOURCE -DPLATFORM_WEB -DGRAPHICS_API_OPENGL_ES2 -Wno-missing-braces -Werror=pointer-arith -fno-strict-aliasing  -std=gnu99 -fPIC -Os -I.  -Iexternal/glfw/include -Iexternal/glfw/deps/mingw
emcc -c rmodels.c -Wall -D_GNU_SOURCE -DPLATFORM_WEB -DGRAPHICS_API_OPENGL_ES2 -Wno-missing-braces -Werror=pointer-arith -fno-strict-aliasing  -std=gnu99 -fPIC -Os -I.  -Iexternal/glfw/include -Iexternal/glfw/deps/mingw
In file included from rmodels.c:111:
./external/par_shapes.h:1133:32: warning: implicit conversion from 'int' to 'float' changes value from 2147483647 to 2147483648 [-Wimplicit-const-int-float-conversion]
 1133 |     float r = (float) rand() / RAND_MAX;
      |                              ~ ^~~~~~~~
/home/runner/work/_temp/347782bb-feec-47ed-8688-38a6103a1214/emsdk-main/upstream/emscripten/cache/sysroot/include/stdlib.h:84:19: note: expanded from macro 'RAND_MAX'
   84 | #define RAND_MAX (0x7fffffff)
      |                   ^~~~~~~~~~
1 warning generated.

[raysan5]

@Lecrapouille There is only one of those warnings that atually can be reviewed.

• mipOffset is actually being used, compilation fails if not defined.
• WindowMaximizeCallback() can be commented, a PR is being sent.
• EmscriptenWindowResizedCallback(), there is an open PR that could require it Changes in preparation for Issue 3372 #3520
• All the other ones belong to external libraries, not raylib, and they should be addressed in respective repos.