Allow tests to fake stdin/stdout/stderr is a console

We've been unable to effectively test cases where stdin/stdout/stderr
are consoles, because in our test cases they generally aren't. Allow the
command line flags `--fake-std{in,out,err}-is-console` to tell the CLI
to pretend that std{in,out,err} is a console.

programs/util.c

@@ -288,6 +288,34 @@ int UTIL_isLink(const char* infilename)
     return 0;
 }
 
+static int g_fakeStdinIsConsole = 0;
+static int g_fakeStderrIsConsole = 0;
+static int g_fakeStdoutIsConsole = 0;
+
+int UTIL_isConsole(FILE* file)
+{
+    if (file == stdin && g_fakeStdinIsConsole)
+        return 1;
+    if (file == stderr && g_fakeStderrIsConsole)
+        return 1;
+    if (file == stdout && g_fakeStdoutIsConsole)
+        return 1;
+    return IS_CONSOLE(file);
+}
+
+void UTIL_fakeStdinIsConsole(void)
+{
+    g_fakeStdinIsConsole = 1;
+}
+void UTIL_fakeStdoutIsConsole(void)
+{
+    g_fakeStdoutIsConsole = 1;
+}
+void UTIL_fakeStderrIsConsole(void)
+{
+    g_fakeStderrIsConsole = 1;
+}
+
 U64 UTIL_getFileSize(const char* infilename)
 {
     stat_t statbuf;