Only the 1st patch is strictly intended for 4.15, paralleling
the recent Dom0 side work (and re-using some of the files
introduced there, for the stubdom build), but later ones may
still want considering.

1: libxenguest: support zstd compressed kernels
2: xen/decompress: make helper symbols static
3: libxenguest: "standardize" LZO kernel decompression code
4: libxenguest: drop redundant decompression declarations
5: libxenguest: simplify kernel decompression

Jan