Failed build against newer libmicrohttpd versions

[hadret]

When trying to compile against newer libmicrohttpd versions it fails with the following errror:

[ 95%] Building C object promhttp/CMakeFiles/promhttp.dir/src/promhttp.c.o
cd /<<PKGBUILDDIR>>/obj-x86_64-linux-gnu/promhttp && /usr/bin/cc -Dpromhttp_EXPORTS -I/<<PKGBUILDDIR>>/promhttp/include -I/<<PKGBUILDDIR>>/
promhttp/../prom/include -I/<<PKGBUILDDIR>>/promhttp/src -I/<<PKGBUILDDIR>>/prom/include -g -O2 -ffile-prefix-map=/<<PKGBUILDDIR>>=. -fstack-protector-strong -Wformat -Werror=format-security -Wdate-time -D_FORTIFY_SOURCE=2 -fPIC -Werror -Wuninitialized -Wall -Wno-unused-label -
std=gnu11 -std=gnu11 -MD -MT promhttp/CMakeFiles/promhttp.dir/src/promhttp.c.o -MF CMakeFiles/promhttp.dir/src/promhttp.c.o.d -o CMakeFiles
/promhttp.dir/src/promhttp.c.o -c /<<PKGBUILDDIR>>/promhttp/src/promhttp.c
/<<PKGBUILDDIR>>/promhttp/src/promhttp.c: In function ‘promhttp_start_daemon’:
/<<PKGBUILDDIR>>/promhttp/src/promhttp.c:64:54: error: passing argument 5 of ‘MHD_start_daemon’ from incompatible pointer type [-Werror=incompatible-pointer-types]
   64 |   return MHD_start_daemon(flags, port, apc, apc_cls, &promhttp_handler, NULL, MHD_OPTION_END);
      |                                                      ^~~~~~~~~~~~~~~~~
      |                                                      |
      |                                                      int (*)(void *, struct MHD_Connection *, const char *, const char *, const char *, const char *, size_t *, void **) {aka int (*)(void *, struct MHD_Connection *, const char *, const char *, const char *, const char *, long unsigned int *, void **)}
In file included from /<<PKGBUILDDIR>>/promhttp/src/promhttp.c:19:
/usr/include/microhttpd.h:2480:45: note: expected ‘MHD_AccessHandlerCallback’ {aka ‘enum MHD_Result (*)(void *, struct MHD_Connection *, co
nst char *, const char *, const char *, const char *, long unsigned int *, void **)’} but argument is of type ‘int (*)(void *, struct MHD_C
onnection *, const char *, const char *, const char *, const char *, size_t *, void **)’ {aka ‘int (*)(void *, struct MHD_Connection *, con
st char *, const char *, const char *, const char *, long unsigned int *, void **)’}
 2480 |                   MHD_AccessHandlerCallback dh, void *dh_cls,
      |                   ~~~~~~~~~~~~~~~~~~~~~~~~~~^~
cc1: all warnings being treated as errors
make[3]: *** [promhttp/CMakeFiles/promhttp.dir/build.make:79: promhttp/CMakeFiles/promhttp.dir/src/promhttp.c.o] Error 1
make[3]: Leaving directory '/<<PKGBUILDDIR>>/obj-x86_64-linux-gnu'
make[2]: *** [CMakeFiles/Makefile2:145: promhttp/CMakeFiles/promhttp.dir/all] Error 2

Breaking change was introduced in libmicrohttpd back in April last year:

Introduce enum MHD_Result for #MHD_YES/#MHD_NO to avoid using 'int' so much.
Note that this change WILL cause compiler warnings until (most) MHD callbacks
in application code change their return type from 'int' to 'enum MHD_Result'.
That said, avoiding possible confusions of different enums is going to make
the code more robust in the future. For conditional compilation, test
for "MHD_VERSION >= 0x00097002". -CG

[wferi]

#72 is the same issue. I noticed this one later, so the pull request only references #72.