std.Target: Bump baseline hexagon model to hexagonv68.

llvm/llvm-project#125584

Author: alexrp

lib/std/Target.zig

@@ -1921,7 +1921,7 @@ pub const Cpu = struct {
                 .avr => &avr.cpu.avr2,
                 .bpfel, .bpfeb => &bpf.cpu.v3,
                 .csky => &csky.cpu.ck810, // gcc/clang do not have a generic csky model.
-                .hexagon => &hexagon.cpu.hexagonv60, // gcc/clang do not have a generic hexagon model.
+                .hexagon => &hexagon.cpu.hexagonv68, // gcc/clang do not have a generic hexagon model.
                 .lanai => &lanai.cpu.v11, // clang does not have a generic lanai model.
                 .loongarch64 => &loongarch.cpu.loongarch64,
                 .m68k => &m68k.cpu.M68000,