#16546 introduced a regression in the configure:
$ ./autogen.sh
$ ./configure --disable-wallet --without-utils --without-daemon --without-gui --disable-tests --disable-bench
...
checking whether to build test_bitcoin... no
checking whether to reduce exports... no
checking that generated files are newer than configure... done
configure: error: conditional "ENABLE_EXTERNAL_SIGNER" was never defined.
Usually this means the macro was only invoked conditionally.
This PR fixes this bug, and refactors indentation to make easier to spot similar bugs in the future.