When compiling with FEATURE_MTAB_SUPPORT disabled, the call to erase_mtab()

When compiling with FEATURE_MTAB_SUPPORT disabled, the call to erase_mtab()
can never be made because useMtab is initialized to 0, and all the other
assignments of that variable assign 0 to it.  Any compiler that can perform
simple constant propogation on local variables will optimize away if statements
testing against that variable, thus the call to erase_mtab() will never be
made.

When compiling for arm using gcc 3.3.3 with FEATURE_MTAB_SUPPORT disabled,
the linker complains that it can't find erase_mtab().  The arm optimizer isn't
exactly the brightest member of the family, and apparently needs to be hit over
the head with a hammer to get its' attention...