Sigbjorn's last optimization (checking for -mno-cygwin only for
mingw32 targets) kicked out -O from the default SRC_CC_OPTS. Apart
from a minor performance hit for some parts of GHC, it yields a GHCi
which can't load HSbase_cbits.o because `lstat' is unknown, at least
on SuSE 7.3.

A little investigation showed the rather arcane reason: lstat and
friends are inline functions and therefore not in libc.so, only in its
static counterpart. Normally this is not a problem at all, but the CPP
INLINE trickery in fptools/libraries/base/cbits/PrelIOUtils.c manages
to get a reference to lstat into PrelIOUtils.o if -O is not given. %-}
A similar problem exists for fstat, too.

Simple solution: Re-add -O to SRC_CC_OPTS, simplifying configure.in a
bit on the way.