[base] Remove truncation in `FT_DivFix'.

* src/base/ftcalc.c (FT_DivFix): Updated.
[base] Use unsigned calculation in `FT_MulDiv'.

* src/base/ftcalc.c (FT_MulDiv): Updated to expand 32-bit range.
[base] Small optimization of `FT_MulFix'.

* src/base/ftcalc.c (FT_MulFix): Loosen up the condition for direct
32-bit calculations.
Minor.
Fix Savannah bug #43033.

* include/config/ftconfig.h, builds/unix/ftconfig.in,
builds/vms/ftconfig.h [FT_LONG64]: Do not disable the macro when
64-bit type is `long'.
Minor.