update-linux-headers: add loongarch and xtensa

These operating systems are newly supported by Zig since the last
linux-headers update.

tools/update-linux-headers.zig

@@ -28,6 +28,7 @@ const LibCTarget = struct {
 const MultiArch = union(enum) {
     arm,
     arm64,
+    loongarch,
     mips,
     powerpc,
     riscv,
@@ -69,6 +70,10 @@ const linux_targets = [_]LibCTarget{
         .name = "m68k",
         .arch = .{ .specific = .m68k },
     },
+    LibCTarget{
+        .name = "loongarch",
+        .arch = .loongarch,
+    },
     LibCTarget{
         .name = "mips",
         .arch = .mips,
@@ -93,6 +98,10 @@ const linux_targets = [_]LibCTarget{
         .name = "x86",
         .arch = .x86,
     },
+    LibCTarget{
+        .name = "xtensa",
+        .arch = .{ .specific = .xtensa },
+    },
 };
 
 const DestTarget = struct {