gnu: lzip: Fix cross-compilation.

Previously the package would build, but the binaries would be build for the
host system, rather than the target.

* gnu/packages/compression.scm (lzip)[arguments]: Set CXX when cross
compiling.

Signed-off-by: Christopher Baines <mail@cbaines.net>

gnu/packages/compression.scm

@@ -632,6 +632,12 @@ some compression ratio).")
               (base32
                "0j59hx72258334rmkwn57ahr6s69nlrx0a5ip1jw2fbiwr12sd63"))))
     (build-system gnu-build-system)
+    (arguments
+     ;; The configure script doesn't recognise the --build or --host
+     ;; arguments, so set CXX here
+     `(,@(if (%current-target-system)
+             `(#:make-flags (list ,(string-append "CXX=" (cxx-for-target))))
+             '())))
     (home-page "https://www.nongnu.org/lzip/lzip.html")
     (synopsis "Lossless data compressor based on the LZMA algorithm")
     (description