btrfs: LLVMLinux: Remove VLAIS

btrfs: LLVMLinux: Remove VLAIS

Replaced the use of a Variable Length Array In Struct (VLAIS) with a C99
compliant equivalent.  This patch instead allocates the appropriate amount of
memory using a char array using the SHASH_DESC_ON_STACK macro.

The new code can be compiled with both gcc and clang.

Signed-off-by: Vinícius Tinti <[email protected]>
Reviewed-by: Jan-Simon Möller <[email protected]>
Reviewed-by: Mark Charlebois <[email protected]>
Signed-off-by: Behan Webster <[email protected]>
Acked-by: Chris Mason <[email protected]>
Acked-by: Herbert Xu <[email protected]>
Cc: "David S. Miller" <[email protected]>