Added support "__attribute__((__vector_size__(B)))" and "__attribute__((ext_vector_type(N)))".

Now we can:
1 - see the return value for functions that return types that use the "ext_vector_size"
2 - dump values that use the vector attributes ("expr $ymm0")
3 - modified the DWARF parser to correctly parse GNU vector types from the DWARF by turning them into clang::Type::ExtVector types instead of just standard arrays

llvm-svn: 178924