Fix bug with high velocities in vents in 32bit builds, fix MingW build

See https://github.com/yquake2/yquake2/issues/71
and https://github.com/yquake2/xatrix/issues/4

In ClientThink(), the float value ent->velocity[i]*8 is saved into
a short and if the value is too big for a short, in 32bit gcc builds
the short is set to SHRT_MIN, resulting in the player being pressed
down instead of up.
Now we put the result in a 32bit int first (which should be big enough)
and assign the int to the short. This still overflows, but with -fwrapv
at least in a defined way (most probably the same way the original
binaries did).

The Makefile now sets $CC to gcc for MingW builds, this should fix
https://github.com/yquake2/xatrix/issues/3

And while I was at it, when the game lib is loaded, it prints the date
it was built, this is especially interesting for our Win32 binaries.

Makefile

@@ -33,6 +33,8 @@ endif
 ifeq ($(OSTYPE), Windows)
 # At this time only i386 is supported on Windows
 ARCH := i386
+# seems like mingw doesn't set CC by default
+CC := gcc
 else
 # Some platforms call it "amd64" and some "x86_64"
 ARCH := $(shell uname -m | sed -e s/i.86/i386/ -e s/amd64/x86_64/)
@@ -66,10 +68,10 @@ endif
 # -MMD to generate header dependencies.
 ifeq ($(OSTYPE), Darwin)
 CFLAGS := -O2 -fno-strict-aliasing -fomit-frame-pointer \
-		  -Wall -pipe -g -arch i386 -arch x86_64 
+		  -Wall -pipe -g -fwrapv -arch i386 -arch x86_64
 else
 CFLAGS := -O2 -fno-strict-aliasing -fomit-frame-pointer \
-		  -Wall -pipe -g -MMD
+		  -Wall -pipe -g -MMD -fwrapv
 endif
 
 # ----------

src/g_save.c

@@ -141,7 +141,7 @@ void
 InitGame(void)
 {
 	gi.dprintf("Game is starting up.\n");
-	gi.dprintf("Game is ctf.\n");
+	gi.dprintf("Game is ctf built on %s.\n", GAMEVERSION, __DATE__);
 
 	gun_x = gi.cvar("gun_x", "0", 0);
 	gun_y = gi.cvar("gun_y", "0", 0);

src/player/client.c

@@ -1620,7 +1620,10 @@ ClientThink(edict_t *ent, usercmd_t *ucmd)
 	for (i = 0; i < 3; i++)
 	{
 		pm.s.origin[i] = ent->s.origin[i] * 8;
-		pm.s.velocity[i] = ent->velocity[i] * 8;
+		/* save to an int first, in case the short overflows
+		 * so we get defined behavior (at least with -fwrapv) */
+		int tmpVel = ent->velocity[i] * 8;
+		pm.s.velocity[i] = tmpVel;
 	}
 
 	if (memcmp(&client->old_pmove, &pm.s, sizeof(pm.s)))