* clang/gcc: enable -pedantic warnings
* suppress a GCC-specific warning in stb_image
* And some clang-specific warnings
* -Wconversion (clang) -Wold-style-cast (clang+gcc)
and fix a few warnings that show up with these (and a few more with
-Wconversion on gcc, even though that's not enabled by default)
* bunch more warnings
* fixes
* remove merge error
Kai Ninomiya
Corentin Wallez