Commit fd5f4ac0813c27c34c387f00044905a859e29e37 broke building ffmpeg with Opencl

[hydra3333]

Summary of the bug:

Building using this commit 2f7ca0b94e49c2bfce8bda3f883766101ebd7a9b
(which is the commit immediately prior to commit fd5f4ac0813c27c34c387f00044905a859e29e37)
works, however building using the broken commit fd5f4ac0813c27c34c387f00044905a859e29e37
with the same configure and build commands, yields the error messages:

undefined reference to `opt_opencl_bench'
undefined reference to `opt_opencl'

How to reproduce:

cross-compile under ubuntu 17.04

./configure --arch=x86 --target-os=mingw32
--cross-prefix=/home/u/Desktop/ffmpeg-windows-build-helpers-withOpenCL-master/sandbox/cross_compilers/mingw-w64-i686/bin/i686-w64-mingw32-
--pkg-config=pkg-config --pkg-config-flags=--static --enable-gray --enable-version3 --disable-debug --disable-doc --disable-htmlpages
--disable-manpages --disable-podpages --disable-txtpages --disable-w32threads --enable-nvenc --enable-cuda --enable-cuvid --enable-d3d11va
--enable-libsoxr --enable-fontconfig --enable-libass --enable-libbluray --enable-iconv --enable-libtwolame --enable-libzvbi --enable-libcaca
--enable-libmodplug --extra-libs=-lstdc++ --extra-libs=-lpng --extra-libs=-loleaut32 --enable-libmp3lame --enable-version3 --enable-zlib
--enable-librtmp --enable-libvorbis --enable-libtheora --enable-libspeex --enable-libopenjpeg --enable-gnutls --enable-libgsm
--enable-libfreetype --enable-libopus --enable-bzlib --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libvo-amrwbenc
--enable-libvpx --enable-libilbc --enable-libwavpack --enable-libwebp --enable-libgme --enable-dxva2 --enable-gray --enable-libopenh264
--enable-libmysofa --enable-libflite --enable-lzma --enable-libsnappy --enable-libzimg --enable-libbs2b --enable-gmp --enable-libfribidi
--enable-cross-compile --enable-pic --extra-libs=-lpsapi --extra-libs=-lspeexdsp --disable-schannel
--extra-cflags=-DLIBTWOLAME_STATIC --extra-cflags=-DMODPLUG_STATIC --extra-cflags=-DCACA_STATIC --enable-gpl --enable-avisynth
--enable-frei0r --enable-filter=frei0r --enable-librubberband --enable-libvidstab --enable-libx264 --enable-libx265 --enable-libxavs
--enable-libxvid --enable-libmfx --enable-avresample --extra-libs=-lpsapi --extra-libs=-lspeexdsp --enable-libcdio
--extra-cflags=-mtune=generic --extra-cflags=-O3 --enable-static --disable-shared
--prefix=/home/u/Desktop/ffmpeg-windows-build-helpers-withOpenCL-master/sandbox/cross_compilers/mingw-w64-i686/i686-w64-mingw32
--enable-nonfree --enable-decklink --enable-libfdk-aac --enable-opencl --enable-runtime-cpudetect --disable-libx264

built on 2017.10.02

[James]

Should be fixed in 3e6829a8aa1ec687086669551aee45743ac25691.