Cannot build EMsoft Release/Debug on Ubuntu 20.04, possibly due to missing import in in msleep.c

[hakonanes]

Trying to build EMsoft Release or Debug on Ubuntu 20.04 with latest commits from EMsoft (7cf74b5) and EMsoftSuperbuild (f28e122) throws this error:

-- Configuring done
-- Generating done
-- Build files have been written to: /home/hakon/kode/emsoft/EMsoftBuild/Release
Scanning dependencies of target EMsoftLib_Generate_StringConstants
Scanning dependencies of target EMsoftLib_Cpp
Scanning dependencies of target DIWorkflowTestPrep
Scanning dependencies of target EMsoftLib_C
[  1%] Generating StringConstants files....
[  1%] Building CXX object Test/CMakeFiles/DIWorkflowTestPrep.dir/DIWorkflowTestPrep.cpp.o
[  1%] Building CXX object EMsoftLib/CMakeFiles/EMsoftLib_Cpp.dir/sht_file.cpp.o
[  1%] Building C object EMsoftLib/CMakeFiles/EMsoftLib_C.dir/msleep.c.o
/home/hakon/kode/emsoft/EMsoft/Source/EMsoftLib/msleep.c: In function ‘msleep’:
/home/hakon/kode/emsoft/EMsoft/Source/EMsoftLib/msleep.c:12:16: error: ‘NULL’ undeclared (first use in this function)
   12 |     select (0, NULL, NULL, NULL, &tv);
      |                ^~~~
/home/hakon/kode/emsoft/EMsoft/Source/EMsoftLib/msleep.c:5:1: note: ‘NULL’ is defined in header ‘<stddef.h>’; did you forget to ‘#include <stddef.h>’?
    4 | #include <sys/time.h>
  +++ |+#include <stddef.h>
    5 | #endif
/home/hakon/kode/emsoft/EMsoft/Source/EMsoftLib/msleep.c:12:16: note: each undeclared identifier is reported only once for each function it appears in
   12 |     select (0, NULL, NULL, NULL, &tv);
      |                ^~~~
make[2]: *** [EMsoftLib/CMakeFiles/EMsoftLib_C.dir/build.make:63: EMsoftLib/CMakeFiles/EMsoftLib_C.dir/msleep.c.o] Error 1
make[1]: *** [CMakeFiles/Makefile2:1499: EMsoftLib/CMakeFiles/EMsoftLib_C.dir/all] Error 2
make[1]: *** Waiting for unfinished jobs....
[  1%] Linking CXX executable ../Bin/DIWorkflowTestPrep
[  1%] Built target DIWorkflowTestPrep
[  1%] Built target EMsoftLib_Generate_StringConstants
[  1%] Linking Fortran static library ../Bin/libEMsoftLib_Cpp.a
[  1%] Built target EMsoftLib_Cpp
make: *** [Makefile:163: all] Error 2

After including the suggested import in msleep.c, the Release (haven't tried Debug) build finished successfully.