The mapping of Windows vs Cygwin/Posix paths is arbitrary and not knowable
from the Posix side, so logic to determine whether to use relative paths
to locate the git-gui library just does not work on Cygwin. Fix this to
unconditionally use absolute path on Cygwin. (This fixes a regression
from 1.5.4).
Signed-off-by: Mark Levedahl <mdl123@verizon.net> Signed-off-by: Shawn O. Pearce <spearce@spearce.org>