Completely convert the pathname expoted in the %msvc_bin_dir_msys%
variable to MSYS format with forward slashes rather than a mixture
of forward and back slashes.
This solves an obscure problem observed by some developers:
[...]
http-push.c
CC remote-curl.o
remote-curl.c
* new script parameters
GEN git-instaweb
sed: -e expression #7, char 155: invalid reference \2 on `s' command's RHS
make: *** [Makefile:2023: git-instaweb] Error 1
Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>