std.Target: add vita os

[vesim987]

No description provided.

[GasInfinity]

shouldn't baseline also be set to the vita's cpu as with 3ds?

         pub fn baseline(arch: Arch, os: Os) *const Model {
             return switch (arch) {
                 .amdgcn => &amdgcn.cpu.gfx906,
                 .arm => switch (os.tag) {
                     .@"3ds" => &arm.cpu.mpcore,
+                    .vita => &arm.cpu.cortex_a9,
                     else => &arm.cpu.baseline,
                 },

[alexrp]

shouldn't baseline also be set to the vita's cpu as with 3ds?

Right, but need clarification on the question above first.