Fix build failure when using Swig 4.

Taken from upstream:
https://github.com/fifengine/fifengine/commit/d14f232f4cd9a00b05d6872957070e8c020f515d

diff --git a/CMakeLists.txt b/CMakeLists.txt
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -893,7 +893,7 @@ if(build-python)
   find_package(PythonLibs ${PYTHON_VERSION_STRING} EXACT)
   include_directories(${PYTHON_INCLUDE_PATH})
 
-  set(CMAKE_SWIG_FLAGS -modern -fastdispatch -dirvtable -nosafecstrings -noproxydel -fastproxy -fastinit -fastunpack -fastquery -modernargs -nobuildnone -keyword -w511 -w473 -w404 -w314)
+  set(CMAKE_SWIG_FLAGS -modern -fastdispatch -dirvtable -noproxydel -fastproxy -fastinit -fastunpack -fastquery -modernargs -keyword -w511 -w473 -w404 -w314)
 
   set_source_files_properties("${PROJECT_BINARY_DIR}/fife.i" PROPERTIES CPLUSPLUS ON)
   set(FIFE_SOURCES ${FIFE_CORE_SRC})
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<tr><td><span title='2016-11-08 14:59:04 +0100'>2016-11-08</span></td><td><a href='/guix/commit/gnu/packages/uml.scm?id=842a1400a7caab2ecb03e9bc9223c7a575c02663'>gnu: Add plantuml.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/uml.scm: New file.
* gnu/local.mk (GNU_SYSTEM_MODULES): Add it.

Signed-off-by: Roel Janssen &lt;roel@gnu.org&gt;
</span></span></td><td>Theodoros Foradis</td></tr>