Extremely long SPDX comment results in a segfault

## Description

[segfault.zip](https://github.com/ethereum/solidity/files/7428026/segfault.zip)

The attached contract produces:

```
../build/solc/solc segfault.sol
Segmentation fault
```

when compiled with solc

On master, using AFL fuzzing. Another discovery using https://github.com/agroce/afl-compiler-fuzzer

## Environment

- Compiler version: 0.8.10-develop.2021.10.27+commit.7ebf71f3.Linux.clang
- Target EVM version (as per compiler settings): N/A
- Framework/IDE (e.g. Truffle or Remix): N/A
- EVM execution environment / backend / blockchain client: N/A
- Operating system: Ubuntu 20.04 in docker

## Steps to Reproduce

Above shows pretty clearly, I think.

Download segfault.zip and begin with the reported ../build/solc/solc segfault.sol command under the stated Ubuntu environment. Trace the crash in the compiler and use the attached contract as the reproducer; done means solc no longer segfaults when compiling it and the regression is covered by a test.

Written by the indexing model from the issue text.