configure: Make the Unifont FONT_SOURCE configurable with --with-unifont=FILE

Font might be located in different location, the default font might
not be available on all systems or other font might be preferred.

Signed-off-by: Mads Kiilerich <mads@kiilerich.com>
Signed-off-by: Richard Marko <srk@48.io>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

configure.ac

@@ -1832,8 +1832,12 @@ fi
 
 AC_SUBST([DJVU_FONT_SOURCE])
 
-FONT_SOURCE=
+AC_ARG_WITH([unifont],
+            AS_HELP_STRING([--with-unifont=FILE],
+                           [set the unifont source [[guessed]]]))
 
+if test "x$with_unifont" = x; then
+  # search in well-known directories
   for ext in pcf pcf.gz bdf bdf.gz ttf ttf.gz; do
     for dir in . /usr/src /usr/share/fonts/X11/misc /usr/share/fonts/unifont /usr/share/fonts/uni /usr/share/fonts/truetype/unifont /usr/share/fonts/misc; do
       if test -f "$dir/unifont.$ext"; then
@@ -1847,6 +1851,9 @@ for ext in pcf pcf.gz bdf bdf.gz ttf ttf.gz; do
       fi
     done
   done
+else
+  FONT_SOURCE="$with_unifont"
+fi
 
 if test x"$enable_build_grub_mkfont" = xno ; then
   FONT_SOURCE=