Philippe 12/01/2022: OpenACC: add correct flags for CPPFLAGS_C in Rules.LXnvhpc.mk

src/Rules.LXnvhpc.mk

-#MNH_LIC Copyright 1994-2021 CNRS, Meteo-France and Universite Paul Sabatier
+#MNH_LIC Copyright 1994-2022 CNRS, Meteo-France and Universite Paul Sabatier
 #MNH_LIC This is part of the Meso-NH software governed by the CeCILL-C licence
 #MNH_LIC version 1. See LICENSE, CeCILL-C_V1-en.txt and CeCILL-C_V1-fr.txt
 #MNH_LIC for details. version 1.
@@ -195,6 +195,7 @@ LDFLAGS    =   -Wl,-warn-once $(OPT)
 CPP = cpp -P -traditional -Wcomment -D_OPENACC=201711
 # CPP = pgfortran -E -Mcpp=noline
 #
+CPPFLAGS_C         = -DLITTLE_endian
 CPPFLAGS_SURFEX    =
 CPPFLAGS_SURCOUCHE +=
 CPPFLAGS_RAD       =