The C++ One Definition Rule states, among others, that all structs must be
defined equivalently in all translation units in a program, or undefined
behavior occurs. This patch doesn't fix all the ODR violations found by GCC
when using link-time optimization, but it fixes some of them, and makes it
possible to build MySQL with LTO at all.

Change-Id: I436d612c73a301c66e83e122f48cf230d621a6f1