linux(4): Use COMPAT_LINUX32 enstead of __ELF_WORD_SIZE.

COMPAT_LINUX32 option is defined for case when building 32-bit Linuxulator
for the 64-bit host. Usage of __ELF_WORD_SIZE is wrong here as it is equal to 32
on i386 too.

MFC after: 1 week

(cherry picked from commit 6f8439db241c7409275d77f5376e8505967bef67)