[Ada] Fix 32/64bit mistake on SYSTEM_INFO component in s-win32

[Ada] Fix 32/64bit mistake on SYSTEM_INFO component in s-win32

The dwActiveProcessorMask field in a SYSTEM_INFO structure on Windows
should be DWORD_PTR, an integer the size of a pointer.

In s-win32, it is currently declared as DWORD. This happens to work on
32bit hosts and is wrong on 64bit hosts, causing mishaps in accesses to
this component and all the following ones.

The proposed correction adds a definition for DWORD_PTR and uses it for
dwActiveProcessorMask in System.Win32.SYSTEM_INFO.

2019-09-18  Olivier Hainque  <hainque@adacore.com>

gcc/ada/

	* libgnat/s-win32.ads (DWORD_PTR): New type, pointer size
	unsigned int.
	(SYSTEM_INFO): Use it for dwActiveProcessorMask.

gcc/testsuite/

	* gnat.dg/system_info1.adb: New testcase.

From-SVN: r275843