Fix build with automake 1.6

automake 1.6 doesn't like using a conditional += to add stuff to foo_LDADD.
Instead you need to conditionally define a variable, then non-conditionally
put that variable in foo_LDADD.

src/or/Makefile.am

@@ -40,14 +40,17 @@ AM_CPPFLAGS = -DSHARE_DATADIR="\"$(datadir)\"" \
 # This seems to matter nowhere but on windows, but I assure you that it
 # matters a lot there, and is quite hard to debug if you forget to do it.
 
+if USE_BUFFEREVENTS
+levent_openssl_lib = -levent_openssl
+else
+levent_openssl_lib =
+endif
+
 tor_LDFLAGS = @TOR_LDFLAGS_zlib@ @TOR_LDFLAGS_openssl@ @TOR_LDFLAGS_libevent@
 tor_LDADD = ./libtor.a ../common/libor.a ../common/libor-crypto.a \
 	../common/libor-event.a \
-	@TOR_ZLIB_LIBS@ -lm @TOR_LIBEVENT_LIBS@ @TOR_OPENSSL_LIBS@ @TOR_LIB_WS32@ @TOR_LIB_GDI@
-
-if USE_BUFFEREVENTS
-tor_LDADD += -levent_openssl
-endif
+	@TOR_ZLIB_LIBS@ -lm @TOR_LIBEVENT_LIBS@ @TOR_OPENSSL_LIBS@ \
+	@TOR_LIB_WS32@ @TOR_LIB_GDI@ $(levent_openssl_lib)
 
 noinst_HEADERS = buffers.h circuitbuild.h circuitlist.h circuituse.h \
 	command.h config.h connection_edge.h connection.h connection_or.h \

src/test/Makefile.am

@@ -21,15 +21,18 @@ test_SOURCES = \
 	test_util.c \
 	tinytest.c
 
+if USE_BUFFEREVENTS
+levent_openssl_lib = -levent_openssl
+else
+levent_openssl_lib =
+endif
+
 test_LDFLAGS = @TOR_LDFLAGS_zlib@ @TOR_LDFLAGS_openssl@ \
         @TOR_LDFLAGS_libevent@
 test_LDADD = ../or/libtor.a ../common/libor.a ../common/libor-crypto.a \
 	../common/libor-event.a \
-	@TOR_ZLIB_LIBS@ -lm @TOR_LIBEVENT_LIBS@ @TOR_OPENSSL_LIBS@ @TOR_LIB_WS32@ @TOR_LIB_GDI@
-
-if USE_BUFFEREVENTS
-test_LDADD += -levent_openssl
-endif
+	@TOR_ZLIB_LIBS@ -lm @TOR_LIBEVENT_LIBS@ @TOR_OPENSSL_LIBS@ \
+	@TOR_LIB_WS32@ @TOR_LIB_GDI@ $(levent_openssl_lib)
 
 noinst_HEADERS = tinytest.h tinytest_macros.h test.h