no-exec-stack on elf32

Dear xvid devs,

the current Xvid source code still produces a shared library with an 
executable stack when compiled with nasm on a 32-bit system. The 
reason is that in the current implementation the output format is 
checked for "elf" and "elf64", whereas the 32-bit variant is called 
"elf32". The patch found here fixes this:
<http://git.debian.org/?p=pkg-multimedia/xvidcore.git;a=blob;f=debian/patches/no-exec-stack-elf32.patch>

"elf" is, however, a valid output format for nasm when used with the 
-f parameter and serves as a shortcut for "elf32". so maybe it makes 
sense to add a separate check for "elf32" instead of replacing the 
check for "elf", but that's up to you. ;)

  - Fabian