Compile warning: ‘DefineCustomConfigVariables’ was used with no prototype before its definition [-Wmissing-prototypes]

[cobolbaby]

root@12a016bff25a:/tmp/pg_jieba/build# make 
Scanning dependencies of target pg_jieba
[ 33%] Building C object CMakeFiles/pg_jieba.dir/pg_jieba.c.o
/tmp/pg_jieba/pg_jieba.c:258:1: warning: ‘DefineCustomConfigVariables’ was used with no prototype before its definition [-Wmissing-prototypes]
  258 | DefineCustomConfigVariables()
      | ^~~~~~~~~~~~~~~~~~~~~~~~~~~
[ 66%] Building CXX object CMakeFiles/pg_jieba.dir/jieba.cpp.o
[100%] Linking CXX shared library pg_jieba.so
[100%] Built target pg_jieba