The title pretty much says it all. Such libraries were present in lib/win32 subdirectory of Win32 binary builds in 0.24.0 and earlier, but seem to be omitted from 0.90.0 onwards. The changelog doesn't say a word about the omission, so I strongly suspect a regression. My suspicion is strengthened by the fact that even some Win32 API-related libs had been missing from 0.90.0 which were put back in 0.90.1 and the changelog marks this as regression.
External libraries and/or the DLL import libraries for them are now separate from the main package, and can be found in the Libraries subdirectory of the Binaries - Windows section:
https://sourceforge.net/projects/fbc/files/Binaries%20-%20Windows/Libraries/
For SDL it's best to use the prebuilt MinGW libraries provided at http://www.libsdl.org/download-1.2.php.
It may indeed be best to reinclude DLL import libraries (which FB provides for external libraries that don't do that themselves) in the main package again in the future, but DLLs themselves or static libraries for that matter can never all be included in the main package, because there simply are too many. (plus in case of BASS the license doesn't allow it)
Until the eventual reinclusion of those DLL import libraries separately downloadable now takes place, I suggest this significant change (i.e. their separation) should be documented somewhere: at least in the changelog, and possibly on the official website too (e.g. in the "Downloads" section).