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>
avformat/rtpdec: Enable GSM RTP depacketization

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>