PYTHON-2331 Fix set_memory_error complier warning

[ShaneHarvey]

bson/buffer.c:36:13: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
   36 | static void set_memory_error() {
      |             ^~~~~~~~~~~~~~~~

Jira: https://jira.mongodb.org/browse/PYTHON-2331

[ShaneHarvey]

Compile is clean now:

 [2020/07/23 00:31:31.453] Running auth tests over ssl with python /opt/python/3.5/bin/python3
 [2020/07/23 00:31:31.453] 3.5.9 (default, Jun 25 2020, 03:29:06)
 [2020/07/23 00:31:31.453] [GCC 4.4.7 20120313 (Red Hat 4.4.7-23)]
 [2020/07/23 00:31:31.765] Coverage.py, version 5.1 with C extension
 [2020/07/23 00:31:31.765] Full documentation is at https://coverage.readthedocs.io
 [2020/07/23 00:31:33.670] INFO: coverage is installed, running tests with coverage...
 [2020/07/23 00:31:33.670] running clean
 [2020/07/23 00:31:33.670] running build_ext
 [2020/07/23 00:31:33.771] building 'bson._cbson' extension
 [2020/07/23 00:31:33.771] creating build
 [2020/07/23 00:31:33.771] creating build/temp.linux-x86_64-3.5
 [2020/07/23 00:31:33.771] creating build/temp.linux-x86_64-3.5/bson
 [2020/07/23 00:31:33.771] gcc -pthread -Wsign-compare -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes -fPIC -Ibson -I/opt/python/3.5/include/python3.5m -c bson/_cbsonmodule.c -o build/temp.linux-x86_64-3.5/bson/_cbsonmodule.o
 [2020/07/23 00:31:34.728] gcc -pthread -Wsign-compare -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes -fPIC -Ibson -I/opt/python/3.5/include/python3.5m -c bson/time64.c -o build/temp.linux-x86_64-3.5/bson/time64.o
 [2020/07/23 00:31:34.868] gcc -pthread -Wsign-compare -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes -fPIC -Ibson -I/opt/python/3.5/include/python3.5m -c bson/buffer.c -o build/temp.linux-x86_64-3.5/bson/buffer.o
 [2020/07/23 00:31:34.931] gcc -pthread -Wsign-compare -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes -fPIC -Ibson -I/opt/python/3.5/include/python3.5m -c bson/encoding_helpers.c -o build/temp.linux-x86_64-3.5/bson/encoding_helpers.o
 [2020/07/23 00:31:34.955] gcc -pthread -shared -Wl,--enable-new-dtags,-rpath,/opt/python/3.5/lib build/temp.linux-x86_64-3.5/bson/_cbsonmodule.o build/temp.linux-x86_64-3.5/bson/time64.o build/temp.linux-x86_64-3.5/bson/buffer.o build/temp.linux-x86_64-3.5/bson/encoding_helpers.o -L/opt/python/3.5/lib -lpython3.5m -o /data/mci/830893c053272b3a7b86493db3357392/src/bson/_cbson.cpython-35m-x86_64-linux-gnu.so
 [2020/07/23 00:31:34.988] building 'pymongo._cmessage' extension
 [2020/07/23 00:31:34.988] creating build/temp.linux-x86_64-3.5/pymongo
 [2020/07/23 00:31:34.988] gcc -pthread -Wsign-compare -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes -fPIC -Ibson -I/opt/python/3.5/include/python3.5m -c pymongo/_cmessagemodule.c -o build/temp.linux-x86_64-3.5/pymongo/_cmessagemodule.o
 [2020/07/23 00:31:35.343] gcc -pthread -Wsign-compare -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes -fPIC -Ibson -I/opt/python/3.5/include/python3.5m -c bson/buffer.c -o build/temp.linux-x86_64-3.5/bson/buffer.o
 [2020/07/23 00:31:35.407] gcc -pthread -shared -Wl,--enable-new-dtags,-rpath,/opt/python/3.5/lib build/temp.linux-x86_64-3.5/pymongo/_cmessagemodule.o build/temp.linux-x86_64-3.5/bson/buffer.o -L/opt/python/3.5/lib -lpython3.5m -o /data/mci/830893c053272b3a7b86493db3357392/src/pymongo/_cmessage.cpython-35m-x86_64-linux-gnu.so
 [2020/07/23 00:31:36.588] running test
 [2020/07/23 00:31:36.588] running egg_info
 [2020/07/23 00:31:36.588] creating pymongo.egg-info

[prashantmital]

I didn't know that methods without any arguments needed to have void for the signature to be correct.
LGTM

[prashantmital]

Good to know https://stackoverflow.com/questions/42125/function-declaration-isnt-a-prototype !