Since that file exists I would say it should be used, it would vastly reduce the risk of bugs due to symbol clashes, like the one mentioned here:
http://users.softlab.ntua.gr/~ttsiod/mp3pro.html
The .sym file needs to be changed since it does not actually work, at least libtool 2.4.2 does not allow empty lines.
Patch with .sym file regenerated from .h file
There were quite a few symbols missing in the .sym file, in particular all id3*_utf16 functions.
Updated patch changes the .sym file to one I manually generated from the .h file.
Thanks, Reimar.
Fixed in our CVS repository (I actually broke your patch in two and committed to my git tree, which then I pushed to our CVS repo):
http://lame.cvs.sf.net/viewvc/lame/lame/include/libmp3lame.sym?r1=1.1&r2=1.2
http://lame.cvs.sf.net/viewvc/lame/lame/libmp3lame/Makefile.am?r1=1.39&r2=1.40