Determining if files linux/memfd.h exist failed with the following output:
Change Dir: /home/dmitry/LibreELEC.tv/build.LibreELEC-S912.aarch64-9.0-devel/kodi-dc587bd/.aarch64-libreelec-linux-gnueabi/CMakeFiles/CMakeTmp

Run Build Command:"/home/dmitry/LibreELEC.tv/build.LibreELEC-S912.aarch64-9.0-devel/toolchain/bin/ninja" "cmTC_1e069"
[1/2] Building C object CMakeFiles/cmTC_1e069.dir/CheckIncludeFiles.c.o
FAILED: CMakeFiles/cmTC_1e069.dir/CheckIncludeFiles.c.o 
/home/dmitry/LibreELEC.tv/build.LibreELEC-S912.aarch64-9.0-devel/toolchain/bin/aarch64-libreelec-linux-gnueabi-gcc   -march=armv8-a+crc+fp+simd -mabi=lp64 -Wno-psabi -mcpu=cortex-a53+crc+fp+simd -fomit-frame-pointer -Wall -pipe -Os -o CMakeFiles/cmTC_1e069.dir/CheckIncludeFiles.c.o   -c CheckIncludeFiles.c
CheckIncludeFiles.c:2:10: fatal error: linux/memfd.h: No such file or directory
 #include <linux/memfd.h>
          ^~~~~~~~~~~~~~~
compilation terminated.
ninja: build stopped: subcommand failed.

Source:
/* */
#include <linux/memfd.h>


int main(void){return 0;}

Determining if the pthread_create exist failed with the following output:
Change Dir: /home/dmitry/LibreELEC.tv/build.LibreELEC-S912.aarch64-9.0-devel/kodi-dc587bd/.aarch64-libreelec-linux-gnueabi/CMakeFiles/CMakeTmp

Run Build Command:"/home/dmitry/LibreELEC.tv/build.LibreELEC-S912.aarch64-9.0-devel/toolchain/bin/ninja" "cmTC_c1ee1"
[1/2] Building C object CMakeFiles/cmTC_c1ee1.dir/CheckSymbolExists.c.o
[2/2] Linking C executable cmTC_c1ee1
FAILED: cmTC_c1ee1 
: && /home/dmitry/LibreELEC.tv/build.LibreELEC-S912.aarch64-9.0-devel/toolchain/bin/aarch64-libreelec-linux-gnueabi-gcc -march=armv8-a+crc+fp+simd -mabi=lp64 -Wno-psabi -mcpu=cortex-a53+crc+fp+simd -fomit-frame-pointer -Wall -pipe -Os  -march=armv8-a+crc+fp+simd -mtune=cortex-a53 -Wl,--as-needed -fuse-ld=gold   -rdynamic CMakeFiles/cmTC_c1ee1.dir/CheckSymbolExists.c.o  -o cmTC_c1ee1   && :
CMakeFiles/cmTC_c1ee1.dir/CheckSymbolExists.c.o:CheckSymbolExists.c:function main: error: undefined reference to 'pthread_create'
CMakeFiles/cmTC_c1ee1.dir/CheckSymbolExists.c.o:CheckSymbolExists.c:function main: error: undefined reference to 'pthread_create'
collect2: error: ld returned 1 exit status
ninja: build stopped: subcommand failed.

File /home/dmitry/LibreELEC.tv/build.LibreELEC-S912.aarch64-9.0-devel/kodi-dc587bd/.aarch64-libreelec-linux-gnueabi/CMakeFiles/CMakeTmp/CheckSymbolExists.c:
/* */
#include <pthread.h>

int main(int argc, char** argv)
{
  (void)argv;
#ifndef pthread_create
  return ((int*)(&pthread_create))[argc];
#else
  (void)argc;
  return 0;
#endif
}

Determining if the function pthread_create exists in the pthreads failed with the following output:
Change Dir: /home/dmitry/LibreELEC.tv/build.LibreELEC-S912.aarch64-9.0-devel/kodi-dc587bd/.aarch64-libreelec-linux-gnueabi/CMakeFiles/CMakeTmp

Run Build Command:"/home/dmitry/LibreELEC.tv/build.LibreELEC-S912.aarch64-9.0-devel/toolchain/bin/ninja" "cmTC_8dd54"
[1/2] Building C object CMakeFiles/cmTC_8dd54.dir/CheckFunctionExists.c.o
[2/2] Linking C executable cmTC_8dd54
FAILED: cmTC_8dd54 
: && /home/dmitry/LibreELEC.tv/build.LibreELEC-S912.aarch64-9.0-devel/toolchain/bin/aarch64-libreelec-linux-gnueabi-gcc -march=armv8-a+crc+fp+simd -mabi=lp64 -Wno-psabi -mcpu=cortex-a53+crc+fp+simd -fomit-frame-pointer -Wall -pipe -Os -DCHECK_FUNCTION_EXISTS=pthread_create  -march=armv8-a+crc+fp+simd -mtune=cortex-a53 -Wl,--as-needed -fuse-ld=gold   -rdynamic CMakeFiles/cmTC_8dd54.dir/CheckFunctionExists.c.o  -o cmTC_8dd54  -lpthreads && :
/home/dmitry/LibreELEC.tv/build.LibreELEC-S912.aarch64-9.0-devel/toolchain/lib/gcc/aarch64-libreelec-linux-gnueabi/7.2.0/../../../../aarch64-libreelec-linux-gnueabi/bin/ld.gold: error: cannot find -lpthreads
CMakeFiles/cmTC_8dd54.dir/CheckFunctionExists.c.o:CheckFunctionExists.c:function main: error: undefined reference to 'pthread_create'
collect2: error: ld returned 1 exit status
ninja: build stopped: subcommand failed.