[build] make clean should delete raygui.c

[SuperUserNameMan]

Hello,

Compiling Raylib 4.5.0 + Raygui 3.6 on Linux :

The #include path in raygui.c is not updated if the value of RAYLIB_MODULE_RAYGUI_PATH is changed on a next compilation attempt.
And make clean does not delete raygui.c.

Same issue might happens with RAYLIB_MODULE_PHYSAC_PATH. (untested)

First attempt :
make RAYLIB_LIBTYPE=SHARED RAYLIB_MODULE_RAYGUI=TRUE

• raygui.c is created with default path.
• compilation might fail because expected default raygui path did not match cruel reality.

Second attempt :
make clean
make RAYLIB_LIBTYPE=SHARED RAYLIB_MODULE_RAYGUI=TRUE RAYLIB_MODULE_RAYGUI_PATH=../../raylib-3.6/src

• compilation fails because raygui.c was neither updated nor cleaned.

[raysan5]

@SuperUserNameMan Feel free to send a PR with the review.

[SuperUserNameMan]

ok, done, but could not test under Windows.