[Dvipng] dvipng-1.15 is broken with freetype-2.9.1

[Ulrich Mueller]

dvipng's configure relies on freetype-config, which is no longer
provided by the most recent freetype version.

>From the CHANGES file of freetype-2.9.1:

    - Use  of  the `freetype-config'  script  to  get compilation  and
      linking  options   is  deprecated   since  it   doesn't  support
      cross-compiling, among other  deficiencies.  Instead, you should
      use the `pkg-config' interface.

      The `configure'  script no longer installs  `freetype-config' by
      default.  For  backwards compatibility,  a new  configure option
      `--enable-freetype-config'   is  provided   that  reverts   this
      decision.

The patch included below should fix the problem.

Of course, aclocal.m4 must also be regenerated. (Maybe it would be
best to move the MAKEINFO* and AC_HAS_KPSE* macros to their own m4
files.)

--- dvipng-1.15-orig/configure.ac
+++ dvipng-1.15/configure.ac
@@ -78,7 +78,8 @@
 AC_CHECK_HEADERS([libgen.h])
 PSFONTS_O=""
 AC_SUBST(PSFONTS_O)
-AC_CHECK_FT2(,[CFLAGS="$FT2_CFLAGS $CFLAGS"
+PKG_CHECK_MODULES([FT2], [freetype2 >= 6.1.0],
+       [CFLAGS="$FT2_CFLAGS $CFLAGS"
        LIBS="$FT2_LIBS $LIBS"
        PSFONTS_O="sfd.o ft.o enc.o fontmap.o tfm.o"
        AC_DEFINE(HAVE_FT2, 1, [Define to 1 if you have freetype2])