configure: Fix debugging on mingw-w64 with gdb

The relocation hack broke debugging on mingw-w64 when using gdb.  This
makes the reloc hack dependent on --disable-debug so it's still enabled
for release builds.

This is simply an immediate fix for the issue of broken debugging, we
should probably still look at the possibility of reverting it outright
if it proves to be more trouble than it's worth.  For now keeping it
enabled for release builds is a reasonable trade off.

Signed-off-by: Alex Smith <theryuu@warpsharp.info>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
