cmd/cgo: give __uint128_t type [16]uint8

The __uint128_t type appears in darwin/arm header files processed by
cgo -godefs in http://golang.org/cl/16045.

Change-Id: I666194c65dee8ea0ae933d2f02a3abe4581c4697
Reviewed-on: https://go-review.googlesource.com/16046Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: David Crawshaw <crawshaw@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/cgo/doc.go

@@ -119,6 +119,7 @@ C.short, C.ushort (unsigned short), C.int, C.uint (unsigned int),
 C.long, C.ulong (unsigned long), C.longlong (long long),
 C.ulonglong (unsigned long long), C.float, C.double.
 The C type void* is represented by Go's unsafe.Pointer.
+The C types __int128_t and __uint128_t are represented by [16]byte.
 
 To access a struct, union, or enum type directly, prefix it with
 struct_, union_, or enum_, as in C.struct_stat.

src/cmd/cgo/gcc.go

@@ -1227,6 +1227,11 @@ func (c *typeConv) Type(dtype dwarf.Type, pos token.Pos) *Type {
 			t.Go = c.int32
 		case 8:
 			t.Go = c.int64
+		case 16:
+			t.Go = &ast.ArrayType{
+				Len: c.intExpr(t.Size),
+				Elt: c.uint8,
+			}
 		}
 		if t.Align = t.Size; t.Align >= c.ptrSize {
 			t.Align = c.ptrSize
@@ -1384,6 +1389,11 @@ func (c *typeConv) Type(dtype dwarf.Type, pos token.Pos) *Type {
 			t.Go = c.uint32
 		case 8:
 			t.Go = c.uint64
+		case 16:
+			t.Go = &ast.ArrayType{
+				Len: c.intExpr(t.Size),
+				Elt: c.uint8,
+			}
 		}
 		if t.Align = t.Size; t.Align >= c.ptrSize {
 			t.Align = c.ptrSize