Remove (not so useful) ld options not supported on Mac OS X

src/Makefile.am

@@ -10,10 +10,6 @@ AM_CPPFLAGS = \
 
 AM_CFLAGS = ${my_CFLAGS}
 
-AM_LDFLAGS = \
-    -Wl,--gc-sections \
-    -Wl,--as-needed
-
 libmodbus_la_SOURCES = \
         modbus.c \
         modbus.h \
@@ -27,7 +23,7 @@ libmodbus_la_SOURCES = \
         modbus-tcp-private.h \
         modbus-version.h
 
-libmodbus_la_LDFLAGS = $(AM_LDFLAGS) -no-undefined \
+libmodbus_la_LDFLAGS = -no-undefined \
         -version-info $(LIBMODBUS_LT_VERSION_INFO)
 
 if OS_WIN32