More consistent use of 64-bit build variable.

Set up TARGET_IS_64_BIT and HOST_IS_64_BIT early so we don't need 2
mechanisms to judge if it's 64-bit build;
Remove the unnecessary 32-bit host variables.

Change-Id: I08d6d4d9ea70f91135fe2ee05463fb9a0d1cee42
8 files changed