Performing C++ SOURCE FILE Test HAVE_CXX_ATOMICS64_WITHOUT_LIB failed with the following output:
Change Dir: /tmp/instance-1/output-1/build/pistache-f2f5a50fbfb5b8ef6cf1d3d2a9d442a8270e375d/CMakeFiles/CMakeTmp

Run Build Command(s):/usr/bin/make cmTC_80c87/fast && make[1]: Entering directory '/tmp/instance-1/output-1/build/pistache-f2f5a50fbfb5b8ef6cf1d3d2a9d442a8270e375d/CMakeFiles/CMakeTmp'
/usr/bin/make -f CMakeFiles/cmTC_80c87.dir/build.make CMakeFiles/cmTC_80c87.dir/build
make[2]: Entering directory '/tmp/instance-1/output-1/build/pistache-f2f5a50fbfb5b8ef6cf1d3d2a9d442a8270e375d/CMakeFiles/CMakeTmp'
Building CXX object CMakeFiles/cmTC_80c87.dir/src.cxx.o
/tmp/instance-1/output-1/host/bin/riscv32-linux-g++ --sysroot=/tmp/instance-1/output-1/host/riscv32-buildroot-linux-gnu/sysroot    -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os -Wall -Wconversion -pedantic -Wextra -Wno-missing-field-initializers -DHAVE_CXX_ATOMICS64_WITHOUT_LIB -std=c++11  -DNDEBUG   -o CMakeFiles/cmTC_80c87.dir/src.cxx.o -c /tmp/instance-1/output-1/build/pistache-f2f5a50fbfb5b8ef6cf1d3d2a9d442a8270e375d/CMakeFiles/CMakeTmp/src.cxx
/tmp/instance-1/output-1/build/pistache-f2f5a50fbfb5b8ef6cf1d3d2a9d442a8270e375d/CMakeFiles/CMakeTmp/src.cxx: In function 'int main()':
/tmp/instance-1/output-1/build/pistache-f2f5a50fbfb5b8ef6cf1d3d2a9d442a8270e375d/CMakeFiles/CMakeTmp/src.cxx:6:12: warning: unused variable 'i' [-Wunused-variable]
   uint64_t i = x.load(std::memory_order_relaxed);
            ^
Linking CXX executable cmTC_80c87
/usr/bin/cmake -E cmake_link_script CMakeFiles/cmTC_80c87.dir/link.txt --verbose=1
/tmp/instance-1/output-1/host/bin/riscv32-linux-g++ --sysroot=/tmp/instance-1/output-1/host/riscv32-buildroot-linux-gnu/sysroot  -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os -Wall -Wconversion -pedantic -Wextra -Wno-missing-field-initializers -DHAVE_CXX_ATOMICS64_WITHOUT_LIB -std=c++11  -DNDEBUG    CMakeFiles/cmTC_80c87.dir/src.cxx.o  -o cmTC_80c87 
/tmp/instance-1/output-1/host/opt/ext-toolchain/bin/../lib/gcc/riscv32-buildroot-linux-gnu/8.3.0/../../../../riscv32-buildroot-linux-gnu/bin/ld: CMakeFiles/cmTC_80c87.dir/src.cxx.o: in function `.L0 ':
src.cxx:(.text.startup+0x10): undefined reference to `__atomic_load_8'
collect2: error: ld returned 1 exit status
make[2]: *** [CMakeFiles/cmTC_80c87.dir/build.make:87: cmTC_80c87] Error 1
make[2]: Leaving directory '/tmp/instance-1/output-1/build/pistache-f2f5a50fbfb5b8ef6cf1d3d2a9d442a8270e375d/CMakeFiles/CMakeTmp'
make[1]: *** [Makefile:121: cmTC_80c87/fast] Error 2
make[1]: Leaving directory '/tmp/instance-1/output-1/build/pistache-f2f5a50fbfb5b8ef6cf1d3d2a9d442a8270e375d/CMakeFiles/CMakeTmp'


Source file was:

#include <atomic>
#include <cstdint>
std::atomic<uint64_t> x (0);
int main() {
  uint64_t i = x.load(std::memory_order_relaxed);
  return 0;
}

Determining if the function __atomic_load_8 exists in the atomic failed with the following output:
Change Dir: /tmp/instance-1/output-1/build/pistache-f2f5a50fbfb5b8ef6cf1d3d2a9d442a8270e375d/CMakeFiles/CMakeTmp

Run Build Command(s):/usr/bin/make cmTC_7759f/fast && make[1]: Entering directory '/tmp/instance-1/output-1/build/pistache-f2f5a50fbfb5b8ef6cf1d3d2a9d442a8270e375d/CMakeFiles/CMakeTmp'
/usr/bin/make -f CMakeFiles/cmTC_7759f.dir/build.make CMakeFiles/cmTC_7759f.dir/build
make[2]: Entering directory '/tmp/instance-1/output-1/build/pistache-f2f5a50fbfb5b8ef6cf1d3d2a9d442a8270e375d/CMakeFiles/CMakeTmp'
Building CXX object CMakeFiles/cmTC_7759f.dir/CheckFunctionExists.cxx.o
/tmp/instance-1/output-1/host/bin/riscv32-linux-g++ --sysroot=/tmp/instance-1/output-1/host/riscv32-buildroot-linux-gnu/sysroot    -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os -Wall -Wconversion -pedantic -Wextra -Wno-missing-field-initializers -DCHECK_FUNCTION_EXISTS=__atomic_load_8  -DNDEBUG   -o CMakeFiles/cmTC_7759f.dir/CheckFunctionExists.cxx.o -c /tmp/instance-1/output-1/build/pistache-f2f5a50fbfb5b8ef6cf1d3d2a9d442a8270e375d/CMakeFiles/CheckLibraryExists/CheckFunctionExists.cxx
<command-line>: error: new declaration 'char __atomic_load_8()' ambiguates built-in declaration 'long long unsigned int __atomic_load_8(const volatile void*, int)' [-fpermissive]
/tmp/instance-1/output-1/build/pistache-f2f5a50fbfb5b8ef6cf1d3d2a9d442a8270e375d/CMakeFiles/CheckLibraryExists/CheckFunctionExists.cxx:7:3: note: in expansion of macro 'CHECK_FUNCTION_EXISTS'
   CHECK_FUNCTION_EXISTS(void);
   ^~~~~~~~~~~~~~~~~~~~~
/tmp/instance-1/output-1/build/pistache-f2f5a50fbfb5b8ef6cf1d3d2a9d442a8270e375d/CMakeFiles/CheckLibraryExists/CheckFunctionExists.cxx: In function 'int main(int, char**)':
/tmp/instance-1/output-1/build/pistache-f2f5a50fbfb5b8ef6cf1d3d2a9d442a8270e375d/CMakeFiles/CheckLibraryExists/CheckFunctionExists.cxx:17:25: error: too few arguments to function 'long long unsigned int __atomic_load_8(const volatile void*, int)'
   CHECK_FUNCTION_EXISTS();
                         ^
make[2]: *** [CMakeFiles/cmTC_7759f.dir/build.make:66: CMakeFiles/cmTC_7759f.dir/CheckFunctionExists.cxx.o] Error 1
make[2]: Leaving directory '/tmp/instance-1/output-1/build/pistache-f2f5a50fbfb5b8ef6cf1d3d2a9d442a8270e375d/CMakeFiles/CMakeTmp'
make[1]: *** [Makefile:121: cmTC_7759f/fast] Error 2
make[1]: Leaving directory '/tmp/instance-1/output-1/build/pistache-f2f5a50fbfb5b8ef6cf1d3d2a9d442a8270e375d/CMakeFiles/CMakeTmp'