libzmq: compatibility workaround for mingw 7

"...with mingw-w64 if you define _FORTIFY_SOUECE to something
    greater than zero you have to link against libssp, either by adding
    -fstack-protector or -lssp, because mingw-w64, unlike GNU libc, does
    not provide fortified functions."

https://github.com/msys2/MINGW-packages/issues/5868

src/libzmq.mk

@@ -13,6 +13,7 @@ define $(PKG)_BUILD
     # build and install the library
     cd '$(BUILD_DIR)' && $(TARGET)-cmake '$(SOURCE_DIR)' \
         -DBUILD_TESTS=OFF \
+        -DCMAKE_CXX_FLAGS='-D_WIN32_WINNT=0x0600 -fstack-protector' \
         -DWITH_DOC=OFF \
         -DWITH_LIBSODIUM=ON \
         -DWITH_PERF_TOOL=OFF
@@ -27,7 +28,7 @@ define $(PKG)_BUILD
      echo 'Requires: libsodium'; \
      echo 'Libs: -lzmq'; \
      echo 'Libs.private: -lws2_32 -lrpcrt4 -liphlpapi'; \
-     echo 'Cflags.private: -DZMQ_STATIC';) \
+     echo 'Cflags.private: -DZMQ_STATIC -fstack-protector';) \
      > '$(PREFIX)/$(TARGET)/lib/pkgconfig/$(PKG).pc'
 
     # test pkg-config
@@ -41,6 +42,7 @@ define $(PKG)_BUILD
     cd '$(BUILD_DIR).test-cmake' && '$(TARGET)-cmake' \
         -DPKG=$(PKG) \
         -DPKG_VERSION=$($(PKG)_VERSION) \
+        -DCMAKE_CXX_FLAGS='-fstack-protector' \
         '$(PWD)/src/cmake/test'
     $(MAKE) -C '$(BUILD_DIR).test-cmake' -j 1 install
 endef