NEON64: enc: no inline asm for clang -O0

[mscdex]

This may not be the best fix, but it does allow compiling of debug builds with clang.

Also, as far as I can tell the NEON32 inline asm is not affected.

Fixes #96

[aklomp]

Hm, as mentioned in #96, I think there might be an easier fix, which is to have clang always load the encoding table with the vld1q_u8_x4 intrinsic. As far as I know, that intrinsic gets compiled correctly by clang, and will allocate four sequential registers. (GCC does not compile the intrinsic correctly and chooses four random registers.)