Commit fb872273 ("arm64: support __int128 on gcc 5+") added support
for arm64 __int128 with gcc with a version-conditional, but neglected to
enable this for clang, which in fact appears to support aarch64 __int128.
This commit therefore enables it if the compiler is clang, using the
same type of makefile conditional used elsewhere in the tree.
Signed-off-by: NJason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: NWill Deacon <will.deacon@arm.com>