57d8b1f1b3 cmake: Avoid fuzzer "multiple definition of `main'" errors (Ryan Ofsky)
Pull request description:
This change builds libraries with `-fsanitize=fuzzer-no-link` instead of `-fsanitize=fuzzer` when the cmake `-DSANITIZERS=fuzzer` option is specified. This is necessary to make fuzzing and IPC cmake options compatible with each other and avoid CI failures in #30975 which enables IPC in the fuzzer CI build:
https://cirrus-ci.com/task/5366255504326656?logs=ci#L2817https://cirrus-ci.com/task/5233064575500288?logs=ci#L2384
The failures can also be reproduced by checking out #31741 and building with `cmake -B build -DBUILD_FOR_FUZZING=ON -DSANITIZERS=fuzzer -DENABLE_IPC=ON` with this fix reverted.
The fix updates the cmake build so when `-DSANITIZERS=fuzzer` is specified, the fuzz test binary is built with `-fsanitize=fuzzer` (so it can use libFuzzer's main function), and libraries are built with `-fsanitize=fuzzer-no-link` (so they can be linked into other executables with their own main functions).
Previously when `-DSANITIZERS=fuzzer` was specified, `-fsanitize=fuzzer` was applied to ALL libraries and executables. This was inappropriate because it made it impossible to build any executables other than the fuzz test executable without triggering link errors:
- `` multiple definition of `main' ``
- `` "undefined reference to `LLVMFuzzerTestOneInput' ``
if they depended on any libraries instrumented for fuzzing.
This was especially a problem when the `ENABLE_IPC` option was set because it made building the `mpgen` code generator impossible so nothing else that depended on generated sources, including the fuzz test binary, could be built either.
This commit was previously part of https://github.com/bitcoin/bitcoin/pull/31741 and had some discussion there starting in https://github.com/bitcoin/bitcoin/pull/31741#pullrequestreview-2619682385
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This PR is part of the [process separation project](https://github.com/bitcoin/bitcoin/issues/28722).
ACKs for top commit:
hebasto:
ACK 57d8b1f1b3, tested on Ubuntu 24.04.
Tree-SHA512: 4011adbc0b08742e83cf7c0560d3d5b5694a863358e6ac9a21239626b4a8fedceca66db34b5a46136a7b26849bb1d8710c894689322ae97e1c407687c3f57d50
4c1906a500