Dendrite fails to build with -flto

*This issue was originally created by [**@Richard-Rogalski**](https://github.com/Richard-Rogalski) at .*

### Background information

- **Dendrite version or git SHA**: 0.12.0
- **SQLite3 or Postgres?**: not built yet
- **Running in Docker?**: no
- **`go version`**: `go version go1.20.2 linux/ppc64le`, `go version go1.19.6 linux/amd64`

### Description

Dendrite fails to build when `-flto` is present in `CGO_CFLAGS`. It can be reproduced with the following command: `CGO_ENABLED=1 CGO_CFLAGS="-O3 -flto -mcpu=native" CGO_CXXFLAGS="${CGO_CFLAGS}" ./build.sh`. Removing `-flto` results in a successful build.

Start with ./build.sh and reproduce the failure using CGO_ENABLED=1, CGO_CFLAGS="-O3 -flto -mcpu=native", and matching CGO_CXXFLAGS on the reported Go and Linux environments. Trace why -flto prevents the build, then verify that ./build.sh succeeds with the flags still present.

Written by the indexing model from the issue text.