Workaround 'ELF_DATA/EM_ALPHA redefined' warning in Android link.h
(revert part of commit a6e4ee9)

* dyn_load.c: Include asm/elf.h and linux/elf-em.h explicitly, and
undefine ELF_DATA and EM_ALPHA (if PLATFORM_ANDROID and
BIONIC_ELFDATA_REDEF_BUG are defined) to avoid "macro redefined"
warnings reported for link.h of Android Bionic.