How to build release/5.3 to match actual release?

I've built the release/5.3 branch of the swift compiler on macOS.
This was done by doing:
./utils/update-checkout --clone --skip-repository swift -j 1 --scheme release/5.3
followed by:
./utils/build-script -R --ios --tvos --watchos --extra-cmake-options=-DSWIFT_DARWIN_ENABLE_STABLE_ABI_BIT:BOOL=TRUE

When I check the version, I get this:
./swiftc -version
Swift version 5.3-dev (LLVM 6811d14c28, Swift 9cfbe5490b)
Target: x86_64-apple-darwin19.6.0

When I look at the built libswiftCore.dylib with otool -l, I see this:
cmd LC_ID_DYLIB
cmdsize 64
name /usr/lib/swift/libswiftCore.dylib (offset 24)
time stamp 1 Wed Dec 31 19:00:01 1969
current version 0.0.0
compatibility version 1.0.0

I'm expecting to see something that matches the installed compiler on both fronts.
For reference, here's the output of the installed compiler version:
steveh-mac:macosx steveh$ xcrun swiftc -version
Apple Swift version 5.3 (swiftlang-1200.0.29.2 clang-1200.0.30.1)
Target: x86_64-apple-darwin19.6.0
and the otool output of libswiftCore.dylib in /usr/lib/swift:
cmd LC_ID_DYLIB
cmdsize 64
name /usr/lib/swift/libswiftCore.dylib (offset 24)
time stamp 1 Wed Dec 31 19:00:01 1969
current version 1103.8.25
compatibility version 1.0.0

How do I get to this point?

The version shipped with Apple products is an internal fork. It is not possible to reproduce it yourself.

I suspected as much. OK. This is inconvenient, but I think I can work with it.