[SDL] valgrind issues on x86_64

[Ryan C. Gordon]

> Are those due to optimization or are they serious problems?

Long standing issue in glibc's dlopen(). My guess is that it's either 
some magic that's harmless but confuses Valgrind, or it's some magic 
that, being harmless, the glibc developers refuse to clean up.

Either way, not an SDL bug. I usually just fill in new Valgrind 
suppressions for dlopen() every time glibc gets upgraded.

--ryan.