update flatbuffers and flatcc versions, fix potential integer overflow in segments exporter

[yeggor]

This update contains minor changes to actualise the library and fixes potential integer overflow.

In the latest version of rizin (rizin 0.7.3) vaddr for .comment and .shstrtab will be 0xffffffffffffffff for true test case:

[0x00002130]> iS
paddr      size   vaddr      vsize  align perm name               type       flags
-------------------------------------------------------------------------------------------
...
0x00008e68 0x180  0x00009e68 0x180  0x0   -rw- .got               PROGBITS   write,alloc
0x00009000 0x80   0x0000a000 0x80   0x0   -rw- .data              PROGBITS   write,alloc
0x00009080 0x0    0x0000a080 0x198  0x0   -rw- .bss               NOBITS     write,alloc
0x00009080 0x4c   ---------- 0x4c   0x0   ---- .comment           PROGBITS   merge,strings
0x000090cc 0xf7   ---------- 0xf7   0x0   ---- .shstrtab          STRTAB

{
  "name": ".comment",
  "size": 76,
  "vsize": 76,
  "perm": "----",
  "type": "PROGBITS",
  "flags": [
    "merge",
    "strings"
  ],
  "paddr": 36992,
  "vaddr": 18446744073709551615
},
{
  "name": ".shstrtab",
  "size": 247,
  "vsize": 247,
  "perm": "----",
  "type": "STRTAB",
  "paddr": 37068,
  "vaddr": 18446744073709551615
}

In the latest version of radare2 (radare2 5.9.6) vaddr for .comment and .shstrtab will be 0:

{
  "name": ".comment",
  "size": 76,
  "vsize": 76,
  "type": "PROGBITS",
  "perm": "----",
  "paddr": 36992,
  "vaddr": 0
},
{
  "name": ".shstrtab",
  "size": 247,
  "vsize": 247,
  "type": "STRTAB",
  "perm": "----",
  "paddr": 37068,
  "vaddr": 0
}

[xorpse]

Thank you, I guesss while we're at it, we should also move to memmap2 and bump the dependencies to the latest versions.