Fixed broken libnDPI build (BUILD_NDPI=ON) if Ninja used as Generator.

Signed-off-by: Toni Uhlig <matzeton@googlemail.com>

.travis.yml

@@ -7,6 +7,8 @@ script:
 - mkdir build-cmake-submodule && cd build-cmake-submodule &&
   cmake .. -DBUILD_EXAMPLES=ON -DBUILD_NDPI=ON -DENABLE_SANITIZER=ON && make && cd ..
 - ./test/run_tests.sh ./libnDPI ./build-cmake-submodule/nDPId-test
+- if ldd build/nDPId | grep -qoEi libndpi; then
+  echo 'nDPId linked against a static libnDPI should not contain a shared linked libnDPI.' >&2; false; fi
 # pkg-config dynamic linked build
 - mkdir build && cd build &&
   PKG_CONFIG_PATH="$(realpath ../build-cmake-submodule/libnDPI/lib/pkgconfig)"

CMakeLists.txt

@@ -69,9 +69,11 @@ if(STATIC_LIBNDPI_INSTALLDIR STREQUAL "" AND BUILD_NDPI)
         libnDPI
         SOURCE_DIR ${CMAKE_CURRENT_SOURCE_DIR}/libnDPI
         CONFIGURE_COMMAND env CC=${CMAKE_C_COMPILER} CFLAGS=${CMAKE_C_FLAGS} LDFLAGS=${CMAKE_EXE_LINKER_FLAGS}
-        MAKE_PROGRAM=${CMAKE_MAKE_PROGRAM} DEST_INSTALL=${CMAKE_BINARY_DIR}/libnDPI
-        ${CMAKE_CURRENT_SOURCE_DIR}/scripts/get-and-build-libndpi.sh
-        BUILD_COMMAND make
+            MAKE_PROGRAM=make DEST_INSTALL=${CMAKE_BINARY_DIR}/libnDPI
+            ${CMAKE_CURRENT_SOURCE_DIR}/scripts/get-and-build-libndpi.sh
+        BUILD_BYPRODUCTS ${CMAKE_BINARY_DIR}/libnDPI/lib/libndpi.a
+        BUILD_COMMAND ""
+        INSTALL_COMMAND ""
         BUILD_IN_SOURCE 1)
 
     add_custom_target(clean-libnDPI