exedir has to be in the c:/foo form, instead of /cygdrive/c/foo,
otherwise a native wrapper set by LO_TRACE won't understand it.

With this, it's possible to use DrMemory on executables invoked by
bin/run.

Change-Id: I5332342fdbf7d9e4859360dd7fbd3d74c149b2dc
(cherry picked from commit 6d78caf6)
Signed-off-by: Michael Stahl <mstahl@redhat.com>