>>> ffmpeg 3.4.5 Extracting
xzcat /home/buildroot/buildroot-test/instance-1/dl/ffmpeg/ffmpeg-3.4.5.tar.xz | tar --strip-components=1 -C /home/buildroot/buildroot-test/instance-1/output/build/ffmpeg-3.4.5   -xf -
>>> ffmpeg 3.4.5 Patching

Applying 0001-ffmpeg-pthreads.patch using patch: 
patching file configure
Hunk #1 succeeded at 2785 (offset 5 lines).
>>> ffmpeg 3.4.5 Updating config.sub and config.guess
for file in config.guess config.sub; do for i in $(find /home/buildroot/buildroot-test/instance-1/output/build/ffmpeg-3.4.5 -name $file); do cp support/gnuconfig/$file $i; done; done
>>> ffmpeg 3.4.5 Patching libtool
>>> ffmpeg 3.4.5 Configuring
(cd /home/buildroot/buildroot-test/instance-1/output/build/ffmpeg-3.4.5/ && rm -rf config.cache && PATH="/home/buildroot/buildroot-test/instance-1/output/host/bin:/home/buildroot/buildroot-test/instance-1/output/host/sbin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games" AR="/home/buildroot/buildroot-test/instance-1/output/host/bin/sparc-linux-ar" AS="/home/buildroot/buildroot-test/instance-1/output/host/bin/sparc-linux-as" LD="/home/buildroot/buildroot-test/instance-1/output/host/bin/sparc-linux-ld" NM="/home/buildroot/buildroot-test/instance-1/output/host/bin/sparc-linux-nm" CC="/home/buildroot/buildroot-test/instance-1/output/host/bin/sparc-linux-gcc" GCC="/home/buildroot/buildroot-test/instance-1/output/host/bin/sparc-linux-gcc" CPP="/home/buildroot/buildroot-test/instance-1/output/host/bin/sparc-linux-cpp" CXX="/home/buildroot/buildroot-test/instance-1/output/host/bin/sparc-linux-g++" FC="/home/buildroot/buildroot-test/instance-1/output/host/bin/sparc-linux-gfortran" F77="/home/buildroot/buildroot-test/instance-1/output/host/bin/sparc-linux-gfortran" RANLIB="/home/buildroot/buildroot-test/instance-1/output/host/bin/sparc-linux-ranlib" READELF="/home/buildroot/buildroot-test/instance-1/output/host/bin/sparc-linux-readelf" STRIP="/home/buildroot/buildroot-test/instance-1/output/host/bin/sparc-linux-strip" OBJCOPY="/home/buildroot/buildroot-test/instance-1/output/host/bin/sparc-linux-objcopy" OBJDUMP="/home/buildroot/buildroot-test/instance-1/output/host/bin/sparc-linux-objdump" AR_FOR_BUILD="/usr/bin/ar" AS_FOR_BUILD="/usr/bin/as" CC_FOR_BUILD="/usr/bin/gcc" GCC_FOR_BUILD="/usr/bin/gcc" CXX_FOR_BUILD="/usr/bin/g++" LD_FOR_BUILD="/usr/bin/ld" CPPFLAGS_FOR_BUILD="-I/home/buildroot/buildroot-test/instance-1/output/host/include" CFLAGS_FOR_BUILD="-O2 -I/home/buildroot/buildroot-test/instance-1/output/host/include" CXXFLAGS_FOR_BUILD="-O2 -I/home/buildroot/buildroot-test/instance-1/output/host/include" LDFLAGS_FOR_BUILD="-L/home/buildroot/buildroot-test/instance-1/output/host/lib -Wl,-rpath,/home/buildroot/buildroot-test/instance-1/output/host/lib" FCFLAGS_FOR_BUILD="" DEFAULT_ASSEMBLER="/home/buildroot/buildroot-test/instance-1/output/host/bin/sparc-linux-as" DEFAULT_LINKER="/home/buildroot/buildroot-test/instance-1/output/host/bin/sparc-linux-ld" CPPFLAGS="-D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64" CFLAGS="-D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64  -Os  " CXXFLAGS="-D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64  -Os  " LDFLAGS="" FCFLAGS=" -Os " FFLAGS=" -Os " PKG_CONFIG="/home/buildroot/buildroot-test/instance-1/output/host/bin/pkg-config" STAGING_DIR="/home/buildroot/buildroot-test/instance-1/output/host/sparc-buildroot-linux-uclibc/sysroot" INTLTOOL_PERL=/usr/bin/perl ac_cv_lbl_unaligned_fail=yes ac_cv_func_mmap_fixed_mapped=yes ac_cv_func_memcmp_working=yes ac_cv_have_decl_malloc=yes gl_cv_func_malloc_0_nonnull=yes ac_cv_func_malloc_0_nonnull=yes ac_cv_func_calloc_0_nonnull=yes ac_cv_func_realloc_0_nonnull=yes lt_cv_sys_lib_search_path_spec="" ac_cv_c_bigendian=yes   ./configure --enable-cross-compile --cross-prefix=/home/buildroot/buildroot-test/instance-1/output/host/bin/sparc-linux- --sysroot=/home/buildroot/buildroot-test/instance-1/output/host/sparc-buildroot-linux-uclibc/sysroot --host-cc="/usr/bin/gcc" --arch="sparc" --target-os="linux" --disable-stripping --pkg-config="/home/buildroot/buildroot-test/instance-1/output/host/bin/pkg-config" --disable-static --enable-shared --prefix=/usr --enable-avfilter --disable-version3 --enable-logging --enable-optimizations --disable-extra-warnings --enable-avdevice --enable-avcodec --enable-avformat --enable-network --disable-gray --enable-swscale-alpha --disable-small --enable-dct --enable-fft --enable-mdct --enable-rdft --disable-crystalhd --disable-dxva2 --enable-runtime-cpudetect --disable-hardcoded-tables --disable-mipsdsp --disable-mipsdspr2 --disable-msa --enable-hwaccels --disable-cuda --disable-cuvid --disable-nvenc --disable-avisynth --disable-frei0r --disable-libopencore-amrnb --disable-libopencore-amrwb --disable-libdc1394 --disable-libgsm --disable-libilbc --disable-libvo-amrwbenc --disable-symver --disable-doc --disable-gpl --disable-nonfree --disable-ffmpeg --disable-ffplay --disable-ffserver --disable-avresample --disable-ffprobe --disable-postproc --enable-swscale --disable-indevs --disable-outdevs --enable-pthreads --enable-zlib --enable-bzlib --disable-libfdk-aac --disable-libcdio --enable-gnutls --disable-openssl --disable-libdrm --disable-libopenh264 --enable-libvorbis --enable-muxer=ogg --enable-encoder=libvorbis --disable-vaapi --disable-vdpau --disable-mmal --disable-omx --disable-omx-rpi --disable-libopencv --enable-libopus --disable-libvpx --disable-libass --disable-libbluray --enable-librtmp --enable-libmp3lame --disable-libmodplug --enable-libspeex --disable-libtheora --enable-libwavpack --disable-iconv --disable-libfreetype --enable-fontconfig --enable-libopenjpeg --disable-libx264 --disable-libx265 --disable-x86asm --disable-mmx --disable-sse --disable-sse2 --disable-sse3 --disable-ssse3 --disable-sse4 --disable-sse42 --disable-avx --disable-avx2 --disable-armv6 --disable-armv6t2 --disable-vfp --disable-neon --disable-altivec --extra-libs=-latomic --enable-pic --cpu="v8"  )
ERROR: librtmp not found using pkg-config

If you think configure made a mistake, make sure you are using the latest
version from Git.  If the latest version fails, report the problem to the
ffmpeg-user@ffmpeg.org mailing list or IRC #ffmpeg on irc.freenode.net.
Include the log file "ffbuild/config.log" produced by configure as this will help
solve the problem.
make: *** [/home/buildroot/buildroot-test/instance-1/output/build/ffmpeg-3.4.5/.stamp_configured] Error 1
make: Leaving directory `/home/buildroot/buildroot-test/instance-1/buildroot'