Show warnings for deprecated declarations

We're about to announce our own set of deprecated functions in libgnucash.
That would be pretty pointless if we also would silence all deprecation warnings
at the same time...

CMakeLists.txt

@@ -568,9 +568,9 @@ set(CMAKE_CXX_FLAGS "-std=gnu++11 ${CMAKE_CXX_FLAGS}")  # FIXME: should be -std=
 
 if (UNIX)
   set( CMAKE_C_FLAGS "-Werror -Wdeclaration-after-statement -Wno-pointer-sign -Wall -Wmissing-prototypes -Wmissing-declarations -Wno-unused ${CMAKE_C_FLAGS}")
-  set( CMAKE_C_FLAGS "-Wno-deprecated-declarations -std=gnu11 -Wno-error=parentheses ${CMAKE_C_FLAGS}")
+  set( CMAKE_C_FLAGS "-Wno-error=deprecated-declarations -std=gnu11 -Wno-error=parentheses ${CMAKE_C_FLAGS}")
   set( CMAKE_CXX_FLAGS "-Werror -Wall -Wmissing-declarations -Wno-unused -Wno-error=parentheses ${CMAKE_CXX_FLAGS}")
-  set( CMAKE_CXX_FLAGS "-Wno-deprecated-declarations ${REGISTER_CXXFLAG} ${CMAKE_CXX_FLAGS}")
+  set( CMAKE_CXX_FLAGS "-Wno-error=deprecated-declarations ${REGISTER_CXXFLAG} ${CMAKE_CXX_FLAGS}")
   set( CMAKE_C_FLAGS_RELEASE "-O3 -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=2 ${CMAKE_C_FLAGS}")
 endif (UNIX)
 if (MINGW)