* build-all.sh: Provide separate environment variables for ELF32
	and UCLIBC multilibs. Disable multilib by default with uClibc.
	* build-elf32.sh: Use ELF32_DISABLE_MULTILIB instead of
	DISABLE_MULTILIB.
	* build-uclibc.sh: Use UCLIBC_DISABLE_MULTILIB instead of
	DISABLE_MULTILIB.