Fix error with NDK r26

Author: equeim

libraries/decoder_ffmpeg/src/main/jni/build_ffmpeg.sh

@@ -113,7 +113,7 @@ make clean
 ./configure \
     --libdir=android-libs/x86_64 \
     --arch=x86_64 \
-    --cpu=x86_64 \
+    --cpu=x86-64 \
     --cross-prefix="${TOOLCHAIN_PREFIX}/x86_64-linux-android${ANDROID_ABI_64BIT}-" \
     --nm="${TOOLCHAIN_PREFIX}/llvm-nm" \
     --ar="${TOOLCHAIN_PREFIX}/llvm-ar" \