Determining if the LWS_WITH_MBEDTLS exist failed with the following output:
Change Dir: /home/buildroot/autobuild/run/instance-3/output-1/build/ttyd-1.6.3/CMakeFiles/CMakeTmp

Run Build Command(s):/usr/bin/make cmTC_693bb/fast && make[1]: Entering directory `/home/buildroot/autobuild/run/instance-3/output-1/build/ttyd-1.6.3/CMakeFiles/CMakeTmp'
/usr/bin/make  -f CMakeFiles/cmTC_693bb.dir/build.make CMakeFiles/cmTC_693bb.dir/build
make[2]: Entering directory `/home/buildroot/autobuild/run/instance-3/output-1/build/ttyd-1.6.3/CMakeFiles/CMakeTmp'
Building C object CMakeFiles/cmTC_693bb.dir/CheckSymbolExists.c.o
/home/buildroot/autobuild/run/instance-3/output-1/host/bin/mips64el-linux-gcc --sysroot=/home/buildroot/autobuild/run/instance-3/output-1/host/mips64el-buildroot-linux-uclibc/sysroot  -I/home/buildroot/autobuild/run/instance-3/output-1/host/mips64el-buildroot-linux-uclibc/sysroot/usr/include/json-c -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os -g0 -D_GNU_SOURCE   -DNDEBUG -o CMakeFiles/cmTC_693bb.dir/CheckSymbolExists.c.o -c /home/buildroot/autobuild/run/instance-3/output-1/build/ttyd-1.6.3/CMakeFiles/CMakeTmp/CheckSymbolExists.c
/home/buildroot/autobuild/run/instance-3/output-1/build/ttyd-1.6.3/CMakeFiles/CMakeTmp/CheckSymbolExists.c: In function 'main':
/home/buildroot/autobuild/run/instance-3/output-1/build/ttyd-1.6.3/CMakeFiles/CMakeTmp/CheckSymbolExists.c:8:19: error: 'LWS_WITH_MBEDTLS' undeclared (first use in this function); did you mean 'LWS_WITH_TLS'?
   return ((int*)(&LWS_WITH_MBEDTLS))[argc];
                   ^~~~~~~~~~~~~~~~
                   LWS_WITH_TLS
/home/buildroot/autobuild/run/instance-3/output-1/build/ttyd-1.6.3/CMakeFiles/CMakeTmp/CheckSymbolExists.c:8:19: note: each undeclared identifier is reported only once for each function it appears in
make[2]: *** [CMakeFiles/cmTC_693bb.dir/CheckSymbolExists.c.o] Error 1
make[2]: Leaving directory `/home/buildroot/autobuild/run/instance-3/output-1/build/ttyd-1.6.3/CMakeFiles/CMakeTmp'
make[1]: *** [cmTC_693bb/fast] Error 2
make[1]: Leaving directory `/home/buildroot/autobuild/run/instance-3/output-1/build/ttyd-1.6.3/CMakeFiles/CMakeTmp'


File /home/buildroot/autobuild/run/instance-3/output-1/build/ttyd-1.6.3/CMakeFiles/CMakeTmp/CheckSymbolExists.c:
/* */
#include <lws_config.h>

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