AXL build errors

[tonyhutter]

Saw this on GCC 10.2.1:

$ make
[  7%] Building C object src/CMakeFiles/axl_o.dir/axl.c.o
/home/hutter2/AXL/src/axl.c: In function ‘AXL_Config_Set’:
/home/hutter2/AXL/src/axl.c:393:31: warning: unused variable ‘kvtree_first_elem_hash’ [-Wunused-variable]
  393 |                 const kvtree* kvtree_first_elem_hash =
      |                               ^~~~~~~~~~~~~~~~~~~~~~
/home/hutter2/AXL/src/axl.c:432:23: warning: unused variable ‘kvtree_first_elem_hash’ [-Wunused-variable]
  432 |         const kvtree* kvtree_first_elem_hash =
      |                       ^~~~~~~~~~~~~~~~~~~~~~
/home/hutter2/AXL/src/axl.c: In function ‘__AXL_Dispatch’:
/home/hutter2/AXL/src/axl.c:947:9: warning: unused variable ‘success’ [-Wunused-variable]
  947 |     int success = kvtree_util_get_int(file_list, AXL_KEY_CONFIG_MKDIR,
      |         ^~~~~~~
[ 14%] Building C object src/CMakeFiles/axl_o.dir/axl_sync.c.o
/home/hutter2/AXL/src/axl_sync.c: In function ‘__axl_sync_start’:
/home/hutter2/AXL/src/axl_sync.c:39:13: warning: variable ‘success’ set but not used [-Wunused-but-set-variable]
   39 |         int success;
      |             ^~~~~~~
[ 21%] Building C object src/CMakeFiles/axl_o.dir/axl_async_datawarp.c.o
[ 28%] Building C object src/CMakeFiles/axl_o.dir/axl_async_bbapi.c.o
[ 35%] Building C object src/CMakeFiles/axl_o.dir/axl_err.c.o
[ 42%] Building C object src/CMakeFiles/axl_o.dir/axl_io.c.o
[ 50%] Building C object src/CMakeFiles/axl_o.dir/axl_util.c.o
[ 57%] Building C object src/CMakeFiles/axl_o.dir/axl_pthread.c.o
/home/hutter2/AXL/src/axl_pthread.c: In function ‘axl_pthread_func’:
/home/hutter2/AXL/src/axl_pthread.c:208:13: warning: variable ‘success’ set but not used [-Wunused-but-set-variable]
  208 |         int success;
      |             ^~~~~~~
[ 57%] Built target axl_o
[ 64%] Linking C static library libaxl.a
[ 64%] Built target axl-static
[ 71%] Linking C shared library libaxl.so
[ 71%] Built target axl
[ 78%] Building C object test/CMakeFiles/test_config.dir/test_config.c.o
[ 85%] Linking C executable test_config
[ 85%] Built target test_config
[ 92%] Building C object test/CMakeFiles/axl_cp.dir/axl_cp.c.o
[100%] Linking C executable axl_cp
[100%] Built target axl_cp