libinn.so.4.0.0 defines the reallocarray symbol, which is also provided by glibc. Please use the function from glibc, rather than supplying your own. A simple recompile against current rawhide might be sufficient, depending on the autoconf logic in the package.
This is fixed in rawhide after latest rebuild (for perl 5.26). Logs (https://kojipkgs.fedoraproject.org//packages/inn/2.6.1/6.fc27/data/logs/x86_64/build.log) show this: [...] checking for reallocarray... yes [...] and the library doesn't contain the symbol anymore: $ objdump -T libinn.so.4.0.0 |grep reallocarray 0000000000000000 DF *UND* 0000000000000000 GLIBC_2.26 reallocarray 000000000001acf0 g DF .text 0000000000000084 Base x_reallocarray