build: disable warnings reported by GCC 9.1.0

Before this commit a debug build fails due to -Werror for me on GCC
9.1.0.

Part of #49.

Author: Totktonada

memcached/CMakeLists.txt

@@ -17,6 +17,13 @@ execute_process(COMMAND ${CMAKE_COMMAND} -E touch_nocreate
 #     ${CMAKE_SOURCE_DIR}/memcached/internal/proto_txt_parser.c
 #     PROPERTIES HEADER_FILE_ONLY true)
 
+# Disable certain compiler warnings.
+set_source_files_properties(
+    ${CMAKE_SOURCE_DIR}/memcached/internal/proto_txt_parser.c
+    PROPERTIES COMPILE_FLAGS -Wno-implicit-fallthrough)
+set_source_files_properties(
+    ${CMAKE_SOURCE_DIR}/memcached/internal/mc_sasl.c
+    PROPERTIES COMPILE_FLAGS -Wno-cast-function-type)
 
 set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wno-deprecated")
 set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-deprecated")