gnu: rlottie: Fix building with GCC.

std::numeric_limits requires "#include <limits>" when building with
cpp_std=c++14. This patch fixes the issue by specifying gnu++17 as
a stdlib.

* gnu/packages/animation.scm (rlottie)[arguments]: Specify -Dcpp_std option.

Signed-off-by: Jonathan Brielmaier <jonathan.brielmaier@web.de>

gnu/packages/animation.scm

@@ -83,7 +83,8 @@
      `(#:configure-flags
        (list
         "-Dlog=true"
-        "-Dtest=true")))
+        "-Dtest=true"
+        "-Dcpp_std=gnu++17")))
     (native-inputs
      (list googletest pkg-config))
     (synopsis "Lottie Animation Library")