configure: Special case libfreetype test

Include the freetype header, in-directly through a macro, like it
is done in the drawtext filter. Do not break if the header is moved.

Unfortunately the drawtext filter included the file where the include
macros are defined in a wrong way. This is not needed and breaks the
build. Remove that #include line too.
Signed-off-by: Alexander Strasser <eclipse7@gmx.net>

configure

@@ -1128,6 +1128,26 @@ require_pkg_config(){
     add_extralibs $(get_safe ${pkg}_libs)
 }
 
+require_libfreetype(){
+    log require_libfreetype "$@"
+    pkg="freetype2"
+    check_cmd $pkg_config --exists --print-errors $pkg \
+      || die "ERROR: $pkg not found"
+    pkg_cflags=$($pkg_config --cflags $pkg)
+    pkg_libs=$($pkg_config --libs $pkg)
+    {
+        echo "#include <ft2build.h>"
+        echo "#include FT_FREETYPE_H"
+        echo "long check_func(void) { return (long) FT_Init_FreeType; }"
+        echo "int main(void) { return 0; }"
+    } | check_ld "cc" $pkg_cflags $pkg_libs \
+      && set_safe ${pkg}_cflags $pkg_cflags \
+      && set_safe ${pkg}_libs   $pkg_libs \
+      || die "ERROR: $pkg not found"
+    add_cflags    $(get_safe ${pkg}_cflags)
+    add_extralibs $(get_safe ${pkg}_libs)
+}
+
 hostcc_o(){
     eval printf '%s\\n' $HOSTCC_O
 }
@@ -4322,7 +4342,7 @@ enabled libfaac           && require2 libfaac "stdint.h faac.h" faacEncGetVersio
 enabled libfdk_aac        && require libfdk_aac fdk-aac/aacenc_lib.h aacEncOpen -lfdk-aac
 flite_libs="-lflite_cmu_time_awb -lflite_cmu_us_awb -lflite_cmu_us_kal -lflite_cmu_us_kal16 -lflite_cmu_us_rms -lflite_cmu_us_slt -lflite_usenglish -lflite_cmulex -lflite"
 enabled libflite          && require2 libflite "flite/flite.h" flite_init $flite_libs
-enabled libfreetype       && require_pkg_config freetype2 "ft2build.h freetype/freetype.h" FT_Init_FreeType
+enabled libfreetype       && require_libfreetype
 enabled libgme            && require  libgme gme/gme.h gme_new_emu -lgme -lstdc++
 enabled libgsm            && { for gsm_hdr in "gsm.h" "gsm/gsm.h"; do
                                    check_lib "${gsm_hdr}" gsm_create -lgsm && break;

libavfilter/vf_drawtext.c

@@ -48,7 +48,6 @@
 #include "video.h"
 
 #include <ft2build.h>
-#include <freetype/config/ftheader.h>
 #include FT_FREETYPE_H
 #include FT_GLYPH_H
 #if CONFIG_FONTCONFIG