Make win variable internal to x.c

There was only a single reference to the `win` variable in st.c, so
exporting that to x.c allows us to rid ourselves of another extern.

Signed-off-by: Devin J. Pohly <djpohly@gmail.com>

st.c

@@ -170,7 +170,6 @@ static char *base64dec(const char *);
 static ssize_t xwrite(int, const char *, size_t);
 
 /* Globals */
-TermWindow win;
 Term term;
 Selection sel;
 int cmdfd;
@@ -1683,11 +1682,8 @@ csihandle(void)
 	case ' ':
 		switch (csiescseq.mode[1]) {
 		case 'q': /* DECSCUSR -- Set Cursor Style */
-			DEFAULT(csiescseq.arg[0], 1);
+			if (xsetcursor(csiescseq.arg[0]))
-			if (!BETWEEN(csiescseq.arg[0], 0, 6)) {
 				goto unknown;
-			}
-			win.cursor = csiescseq.arg[0];
 			break;
 		default:
 			goto unknown;

st.h

@@ -201,7 +201,6 @@ void *xrealloc(void *, size_t);
 char *xstrdup(char *);
 
 /* Globals */
-extern TermWindow win;
 extern Term term;
 extern Selection sel;
 extern int cmdfd;

win.h

@@ -14,5 +14,6 @@ void xhints(void);
 void xloadcols(void);
 int xsetcolorname(int, const char *);
 void xsettitle(char *);
+int xsetcursor(int);
 void xsetpointermotion(int);
 void xsetsel(char *, Time);

x.c

@@ -187,6 +187,7 @@ static void (*handler[LASTEvent])(XEvent *) = {
 static DC dc;
 static XWindow xw;
 static XSelection xsel;
+static TermWindow win;
 
 enum window_state {
 	WIN_VISIBLE = 1,
@@ -1615,6 +1616,16 @@ xsetpointermotion(int set)
 	XChangeWindowAttributes(xw.dpy, xw.win, CWEventMask, &xw.attrs);
 }
 
+int
+xsetcursor(int cursor)
+{
+	DEFAULT(cursor, 1);
+	if (!BETWEEN(cursor, 0, 6))
+		return 1;
+	win.cursor = cursor;
+	return 0;
+}
+
 void
 xseturgency(int add)
 {