Honour MAKE variable for systems with make != GNU make (eg fbsd)

Index: libsndfile-1.0.25/configure.ac
===================================================================
--- libsndfile-1.0.25.orig/configure.ac
+++ libsndfile-1.0.25/configure.ac
@@ -701,5 +701,5 @@ if test x$prefix != "x/usr" ; then
 	echo
 	fi
 
-(cd src && make genfiles)
-(cd tests && make genfiles)
+(cd src && ${MAKE-make} genfiles)
+(cd tests && ${MAKE-make} genfiles)