move more flags into configure

since BwTree is an optional backend, the BwTree flags should be selected
at configure time

Makefile.am

@@ -32,7 +32,6 @@ noinst_HEADERS = src/datastore.h \
 		 src/BwTree/src/bloom_filter.h \
 		 src/BwTree/src/sorted_small_set.h
 
-lib_libkvserver_la_CPPFLAGS = ${CPPFLAGS} -I${srcdir}/src/BwTree/src
 
 lib_libkvgroupserver_la_SOURCES = src/kvgroup-server.cc
 lib_libkvgroupserver_la_CPPFLAGS = ${CPPFLAGS}

configure.ac

@@ -97,6 +97,8 @@ fi
 
 if test "x${bwtree_backend}" == xyes ; then
 	AC_DEFINE([USE_BWTREE], 1, [use BwTree backend])
+	CPPFLAGS="-I${srcdir}/src/BwTree/src ${CPPFLAGS}"
+
 	CXXFLAGS="-pthread -std=c++11 -g -Wall -mcx16 -Wno-invalid-offsetof ${CXXFLAGS}"
 	berkeleydb_backend=no
 	leveldb_backend=no