fix FreeBSD bundled protobuf build if system one is present (#12552)

* fix FreeBSD build where both bundled and pkg protobuf installed and bundled requested

configure.ac

@@ -280,11 +280,14 @@ fi
 # -----------------------------------------------------------------------------
 # operating system detection
 
+originalCFLAGS="${CFLAGS}"
 AC_MSG_CHECKING([operating system])
 case "$host_os" in
 freebsd*)
     build_target=freebsd
-    CFLAGS="${CFLAGS} -I/usr/local/include -L/usr/local/lib"
+    OPTIONAL_OS_DEP_CFLAGS="-I/usr/local/include"
+    CFLAGS="${CFLAGS} ${OPTIONAL_OS_DEP_CFLAGS}"
+    LDFLAGS="${LDFLAGS} -L/usr/local/lib"
     ;;
 darwin*)
     build_target=macos
@@ -1514,7 +1517,7 @@ test "${enable_lto}" = "yes" -a "${have_lto}" != "yes" && \
 AC_MSG_CHECKING([if LTO should be enabled])
 if test "${enable_lto}" != "no" -a "${have_lto}" = "yes"; then
     enable_lto="yes"
-    CFLAGS="${CFLAGS} -flto"
+    OPTIONAL_LTO_CFLAGS="-flto"
 else
     enable_lto="no"
 fi
@@ -1565,11 +1568,12 @@ AC_SUBST([logdir])
 AC_SUBST([pluginsdir])
 AC_SUBST([webdir])
 
-CFLAGS="${CFLAGS} ${OPTIONAL_PROTOBUF_CFLAGS} ${OPTIONAL_MATH_CFLAGS} ${OPTIONAL_NFACCT_CFLAGS} ${OPTIONAL_ZLIB_CFLAGS} ${OPTIONAL_UUID_CFLAGS} \
+CFLAGS="${originalCFLAGS} ${OPTIONAL_LTO_CFLAGS} ${OPTIONAL_PROTOBUF_CFLAGS} ${OPTIONAL_MATH_CFLAGS} ${OPTIONAL_NFACCT_CFLAGS} \
+    ${OPTIONAL_ZLIB_CFLAGS} ${OPTIONAL_UUID_CFLAGS} \
     ${OPTIONAL_LIBCAP_CFLAGS} ${OPTIONAL_IPMIMONITORING_CFLAGS} ${OPTIONAL_CUPS_CFLAGS} ${OPTIONAL_XENSTAT_FLAGS} \
     ${OPTIONAL_KINESIS_CFLAGS} ${OPTIONAL_PUBSUB_CFLAGS} ${OPTIONAL_PROMETHEUS_REMOTE_WRITE_CFLAGS} \
     ${OPTIONAL_MONGOC_CFLAGS} ${LWS_CFLAGS} ${OPTIONAL_JSONC_STATIC_CFLAGS} ${OPTIONAL_BPF_CFLAGS} ${OPTIONAL_JUDY_CFLAGS} \
-    ${OPTIONAL_ACLK_CFLAGS} ${OPTIONAL_ML_CFLAGS} ${OPTIONAL_ML_TESTS_CFLAGS}"
+    ${OPTIONAL_ACLK_CFLAGS} ${OPTIONAL_ML_CFLAGS} ${OPTIONAL_ML_TESTS_CFLAGS} ${OPTIONAL_OS_DEP_CFLAGS}"
 
 CXXFLAGS="${CFLAGS} ${CXX11FLAG}"