Using WinMerge as the git Diff/Merge Tool on Windows 64bit

.gitconfig

[mergetool]
    prompt = false
    keepBackup = false
    keepTemporaries = false

[merge]
    tool = winmerge

[mergetool "winmerge"]
    name = WinMerge
    trustExitCode = true
    cmd = "/c/Program\\ Files\\ \\(x86\\)/WinMerge/WinMergeU.exe" -u -e -dl \"Local\" -dr \"Remote\" $LOCAL $REMOTE $MERGED

[diff]
    tool = winmerge

[difftool "winmerge"]
    name = WinMerge
    trustExitCode = true
    cmd = "/c/Program\\ Files\\ \\(x86\\)/WinMerge/WinMergeU.exe" -u -e $LOCAL $REMOTE

Finally this worked for me

[mergetool "winmerge"]
name = WinMerge
trustExitCode = true
cmd = ""C:/Program Files (x86)/WinMerge/WinMergeU.exe" "$LOCAL" "$REMOTE" "$MERGED" >/dev/null 2>&1"

[diff]
tool = winmerge
[difftool "winmerge"]
name = WinMerge
trustExitCode = true
cmd = ""C:/Program Files (x86)/WinMerge/WinMergeU.exe" "$REMOTE" "$LOCAL" >/dev/null 2>&1"

command to diff
"git difftool"
and from winmerge I manually merge with winmerge functionality