Remove FLAG_STDERR_TTY.

It really had no need to be a global process flag at all: it's used to
signal to uxcons.c that stderr_tty_init() ought to check whether
stderr is a tty (in order to save its termios across interactive
prompts and so forth). But the only _caller_ of stderr_tty_init is
Unix Plink, which always sets that flag! So we already have a
perfectly good system for signalling to uxcons.c that you'd like
stderr_tty_init to do something: _whether you call it or not_.

unix/unix.h

@@ -101,18 +101,6 @@ unsigned long getticks(void);
 #define WCHAR wchar_t
 #define BYTE unsigned char
 
-/*
- * Unix-specific global flag
- *
- * FLAG_STDERR_TTY indicates that standard error might be a terminal and
- * might get its configuration munged, so anything trying to output plain
- * text (i.e. with newlines in it) will need to put it back into cooked
- * mode first.  Applications setting this flag should also call
- * stderr_tty_init() before messing with any terminal modes, and can call
- * premsg() before outputting text to stderr and postmsg() afterwards.
- */
-#define FLAG_STDERR_TTY 0x1000
-
 #define PLATFORM_CLIPBOARDS(X)                            \
     X(CLIP_PRIMARY, "X11 primary selection")              \
     X(CLIP_CLIPBOARD, "XDG clipboard")                    \
@@ -305,7 +293,7 @@ extern char *pty_osx_envrestore_prefix;
 
 /* Things provided by uxcons.c */
 struct termios;
-void stderr_tty_init(void);
+void stderr_tty_init(void); /* call at startup if stderr might be a tty */
 void premsg(struct termios *);
 void postmsg(struct termios *);
 

unix/uxcons.c

@@ -26,7 +26,7 @@ static bool stderr_is_a_tty;
 void stderr_tty_init()
 {
     /* Ensure that if stderr is a tty, we can get it back to a sane state. */
-    if ((flags & FLAG_STDERR_TTY) && isatty(STDERR_FILENO)) {
+    if (isatty(STDERR_FILENO)) {
         stderr_is_a_tty = true;
         tcgetattr(STDERR_FILENO, &orig_termios_stderr);
     }

unix/uxplink.c

@@ -603,7 +603,7 @@ int main(int argc, char **argv)
     stderr_bs = BinarySink_UPCAST(&stderr_bcs);
     outgoingeof = EOF_NO;
 
-    flags = FLAG_STDERR_TTY;
+    flags = 0;
     cmdline_tooltype |=
         (TOOLTYPE_HOST_ARG |
          TOOLTYPE_HOST_ARG_CAN_BE_SESSION |