os_win32/popen_win32.cpp, os_win32/popen.h: New popen()/pclose() for Windows.

Unlike MSVCRT _popen(), it does not open a new console.
os_win32.cpp: Remove run_cmd(), use popen() instead.
os_win32/daemon_win32.cpp, os_win32/daemon_win32.h: Remove daemon_spawn().
smartd.cpp: Remove _WIN32 specific usage of daemon_spawn(), use generic code
with popen() also on Windows.
Makefile.am, os_win32/vc14/smart*.vcxproj*: Add new files.

git-svn-id: https://svn.code.sf.net/p/smartmontools/code/trunk@4818 4ea69e1a-61f1-4043-bf83-b5c94c648137