Fails to compile on FreeBSD

[probonopd]

% gmake
gcc  -D__FreeBSD__=10 -D_FILE_OFFSET_BITS=64 -I/usr/local/include/fuse -std=c99 -I. -Wno-int-to-pointer-cast -Wno-pointer-to-int-cast -Wno-multichar fusemfs.c -L/usr/lib -liconv -L/usr/local/lib -lfuse -Llibmfs -Llibres -lmfs -lres -o fusemfs
<command-line>: warning: "__FreeBSD__" redefined
<built-in>: note: this is the location of the previous definition
fusemfs.c: In function 'mfs_to_utf8':
fusemfs.c:113:27: warning: passing argument 2 of 'libiconv' from incompatible pointer type [-Wincompatible-pointer-types]
  113 |     iconv(_fusemfs_iconv, (const char **restrict)&in, &len, &outp, &outleft);
      |                           ^~~~~~~~~~~~~~~~~~~~~~~~~~
      |                           |
      |                           const char **
In file included from fusemfs.c:32:
/usr/local/include/iconv.h:84:43: note: expected 'char **' but argument is of type 'const char **'
   84 | extern size_t iconv (iconv_t cd,  char* * inbuf, size_t *inbytesleft, char* * outbuf, size_t *outbytesleft);
      |                                   ~~~~~~~~^~~~~
fusemfs.c: In function 'utf8_to_mfs':
fusemfs.c:132:27: warning: passing argument 2 of 'libiconv' from incompatible pointer type [-Wincompatible-pointer-types]
  132 |     iconv(_fusemfs_vnoci, &in, &len, &outp, &outleft);
      |                           ^~~
      |                           |
      |                           const char **
In file included from fusemfs.c:32:
/usr/local/include/iconv.h:84:43: note: expected 'char **' but argument is of type 'const char **'
   84 | extern size_t iconv (iconv_t cd,  char* * inbuf, size_t *inbytesleft, char* * outbuf, size_t *outbytesleft);
      |         

cc @crees