Philippe 13/01/2022: BITREP: correct rule for BITREP compilation

src/Makefile.MESONH.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.
@@ -677,7 +677,7 @@ export NETCDF_INCLUDE NETCDF_LIBRARY F90 CC
 # functions (EXP, LOG, POWER...) especially for
 # CPU / GPU comparisons
 #
-ifdef MNH_BITREP
+ifeq "$(MNH_BITREP)" "YES"
 DIR_MASTER += LIB/BITREP
 VPATH += LIB/BITREP
 OBJS_LISTE_MASTER += br_transcendentals.o