dhewm#625 (comment)
confirms that it's broken

for the fix, see
ocornut/imgui#6732 (comment)
ocornut/imgui#5190

to avoid unaligned reads from class members of idClass or its
derived classes

All that code is kinda obfuscated, but the integer passing was plain
wrong (if sizeof(int) != sizeof(intptr_t), esp. noticeable on
 Big Endian).
data[i] is used by Callbacks.cpp, and for everything but floats it's
passed directly as an argument (interpreted as either an integer or
a pointer to idVec3 or whatever).
So storing an int in there with `( *( int * )&data[ i ] ) = int(...)`
only sets the first 4 bytes of that intptr_t, which is 8 bytes on 64bit
machines. On Little Endian that just happens to work, on Big Endian
it's the wrong 4 bytes.

idInterpreter::Push() is used only for int and (reinterpreted) float
values, not pointers (as far as I can tell), so 32bit values on all
relevant platforms.
It stored its value as intptr_t at `&localstack[ localstackUsed ]` - on
64bit platforms intptr_t is 64bit.
Unfortunately, all code reading from the stack just get got a pointer
to `&localstack[ localstackUsed ]` in the type they want to read
(like `int*` or `float*`) and read that. On Little Endian that happens
to work, on 64bit Big Endian it reads the wrong 4 bytes of the intptr_t,
so it doesn't work.

fixes dhewm#625, dhewm#472