Add vec_extract expanders for all valid pairs of vector types.

gcc/ChangeLog:

	* config/gcn/gcn-protos.h (get_exec): Add prototypes for two variants.
	* config/gcn/gcn-valu.md
	(vec_extract<V_ALL:mode><V_ALL_ALT:mode>): New define_expand.
	* config/gcn/gcn.cc (get_exec): Export the existing function. Add a
	new overload variant.
---
 gcc/config/gcn/gcn-protos.h |  2 ++
 gcc/config/gcn/gcn-valu.md  | 34 ++++++++++++++++++++++++++++++++++
 gcc/config/gcn/gcn.cc       |  9 ++++++++-
 3 files changed, 44 insertions(+), 1 deletion(-)