Cleanup code for clang

Set clang as the default compiler for sw/vec repo.

clang only supports RVV v0.10, which requires the vset[i]vl[i] syntax of
vset[i]vl[i] rd, avl, e[8|16|32], m[1|2|4|8], [ta|tu], [ma|mu]

Set the default {tu, mu} based on the spec if not specified
Disable e64 and fractional lmul since it may not work yet.

Change-Id: I7edc12897aff2fa2b27eb9050e276e17906f5570
14 files changed