[util] Use setlinebuf() if present

To work around mysterious bug on OS X.

Fixes https://github.com/harfbuzz/harfbuzz/issues/727

configure.ac

@@ -69,7 +69,7 @@ GTK_DOC_CHECK([1.15],[--flavour no-tmpl])
 ])
 
 # Functions and headers
-AC_CHECK_FUNCS(atexit mprotect sysconf getpagesize mmap isatty newlocale strtod_l)
+AC_CHECK_FUNCS(atexit mprotect sysconf getpagesize mmap isatty newlocale strtod_l setlinebuf)
 AC_CHECK_HEADERS(unistd.h sys/mman.h xlocale.h)
 
 # Compiler flags
@@ -355,9 +355,7 @@ if $have_freetype; then
 	AC_DEFINE(HAVE_FREETYPE, 1, [Have FreeType 2 library])
 	save_libs=$LIBS
 	LIBS="$LIBS $FREETYPE_LIBS"
-	AC_CHECK_FUNCS(FT_Get_Var_Blend_Coordinates)
-	AC_CHECK_FUNCS(FT_Set_Var_Blend_Coordinates)
-	AC_CHECK_FUNCS(FT_Done_MM_Var)
+	AC_CHECK_FUNCS(FT_Get_Var_Blend_Coordinates FT_Set_Var_Blend_Coordinates FT_Done_MM_Var)
 	LIBS=$save_libs
 fi
 AM_CONDITIONAL(HAVE_FREETYPE, $have_freetype)

util/options.cc

@@ -780,7 +780,11 @@ text_options_t::get_line (unsigned int *len)
     gs = g_string_new (nullptr);
   }
 
-  setvbuf(fp, NULL, _IOLBF, BUFSIZ); //setlinebuf (fp);
+#ifdef HAVE_SETLINEBUF
+  setlinebuf (fp);
+#else
+  setvbuf(fp, NULL, _IOLBF, BUFSIZ);
+#endif
 
   g_string_set_size (gs, 0);
   char buf[BUFSIZ];
@@ -819,7 +823,11 @@ output_options_t::get_file_handle (void)
     fail (false, "Cannot open output file `%s': %s",
 	  g_filename_display_name (output_file), strerror (errno));
 
-  setvbuf(fp, NULL, _IOLBF, BUFSIZ); //setlinebuf (fp);
+#ifdef HAVE_SETLINEBUF
+  setlinebuf (fp);
+#else
+  setvbuf(fp, NULL, _IOLBF, BUFSIZ);
+#endif
 
   return fp;
 }