Add AM_LDFLAGS to LDFLAGS

configure.ac

@@ -43,8 +43,8 @@ AC_SUBST(LIBMODBUS_VERSION)
 LIBMODBUS_LD_CURRENT=4
 LIBMODBUS_LD_REVISION=0
 LIBMODBUS_LD_AGE=0
-LIBMODBUS_LT_LDFLAGS="-version-info $LIBMODBUS_LD_CURRENT:$LIBMODBUS_LD_REVISION:$LIBMODBUS_LD_AGE"
-AC_SUBST(LIBMODBUS_LT_LDFLAGS)
+LIBMODBUS_LT_VERSION_INFO=$LIBMODBUS_LD_CURRENT:$LIBMODBUS_LD_REVISION:$LIBMODBUS_LD_AGE
+AC_SUBST(LIBMODBUS_LT_VERSION_INFO)
 
 # Checks for programs.
 AC_PROG_CC

src/Makefile.am

@@ -1,6 +1,6 @@
 lib_LTLIBRARIES = libmodbus.la
 libmodbus_la_SOURCES = modbus.c modbus.h
-libmodbus_la_LDFLAGS = $(LIBMODBUS_LT_LDFLAGS)
+libmodbus_la_LDFLAGS = $(AM_LDFLAGS) -version-info $(LIBMODBUS_LT_VERSION_INFO)
 
 # Include files to install
 libmodbusincludedir = $(includedir)