[OPTIM] force inlining of large functions with gcc >= 3

[OPTIM] force inlining of large functions with gcc >= 3

GCC 3 and above do not inline large functions, which is a problem
with ebtree where most core functions are inlined.

This simple patch has both reduced code size and increased speed.
It should be back-ported to ebtree.
(cherry picked from commit 707d3da01f8475d5c172d347a73bd9e947076df6)