jsoncpp: add workaround for builds with GCC >= 6.x

src/jsoncpp.mk

@@ -10,6 +10,9 @@ $(PKG)_FILE     := $(PKG)-$($(PKG)_VERSION).tar.gz
 $(PKG)_URL      := https://github.com/open-source-parsers/jsoncpp/archive/$($(PKG)_VERSION).tar.gz
 $(PKG)_DEPS     := gcc
 
+# workaround for builds with GCC >= 6.x
+$(PKG)_CXXFLAGS := -Wno-error=conversion -Wno-error=shift-negative-value
+
 define $(PKG)_UPDATE
     $(WGET) -q -O- 'https://github.com/open-source-parsers/jsoncpp/archive/' | \
     $(SED) -n 's,.*/\([0-9][^"]*\)/"\.tar.*,\1,p' | \
@@ -22,6 +25,7 @@ define $(PKG)_BUILD
     cd '$(1)/build' && cmake .. \
         -DCMAKE_TOOLCHAIN_FILE='$(CMAKE_TOOLCHAIN_FILE)' \
         -DJSONCPP_WITH_POST_BUILD_UNITTEST=OFF \
+        -DCMAKE_CXX_FLAGS="$($(PKG)_CXXFLAGS)" \
         -DBUILD_STATIC_LIBS=$(if $(BUILD_STATIC),true,false) \
         -DBUILD_SHARED_LIBS=$(if $(BUILD_STATIC),false,true)
     $(MAKE) -C '$(1)/build' -j '$(JOBS)' install