[Ada] Force even timestamp in Windows ALI files

[Ada] Force even timestamp in Windows ALI files

Old versions forced even file timestamp in Windows in
GNAT.OS_Lib.GM_Split implementation. We removed this time distortion in
GNAT.OS_Lib.GM_Split a few commits. But gprbuild became unnecessary
recompiling the sources in 50% cases, when the source has odd file
timestamp. This commit is restoring the compatibility between new
gprbuild and old GNAT compilers.

2019-09-17  Dmitriy Anisimkov  <anisimko@adacore.com>

gcc/ada/

	* make_util.ads (On_Windows): Move...
	* osint.ads (On_Windows): There.
	* osint.adb (OS_Time_To_GNAT_Time): If odd incremented on
	Windows before conversion to Time_Stamp_Type.

From-SVN: r275789