Problem:

After upgrading to Snow Leopard, I had to rebuild/reinstall MacPorts and RubyGems as recommended. While doing this, I found that sqlite3-ruby gem install failed with errors related to extconf.rb file.

Solution:

Not sure why this works but I found a working solution at StackOverflow which replaces:

/usr/local/lib/libsqlite3.dylib

with a symbolic link to one that came with XCode for Snow Leopard:

/Developer/SDKs/MacOSX10.6.sdk/usr/lib/libsqlite3.0.dylib

You can find the full ‘ln’ command at StackOverlow page above but be sure to rename the original in case you need to restore it.