fix(util/realpath): rename realpath to lrealpath

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
fix(util/lean_path): use unix style paths when using cygwin

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
fix(util/realpath): realpath on cygwin

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>