```
ninja check check-functional
```
Run this before and after patch:
```
./src/bench/bitcoin-bench -filter=BlockToJsonVerbose
```
Observe ~3-4% speedup.
Verify internal linkage:
```
cmake -GNinja -DCMAKE_CXX_FLAGS="-emit-llvm -S" ..
ninja univalue
grep "define internal" src/univalue/libunivalue.a
```
I was only able to verify internal linkage for `writeStream()` and `json_escape()`. Not the other helper functions.