Issue with toupper when compiling

Thought I'd check in and see how things are going, but didn't manage to compile.. this time it's toupper causing an issue.

This is on Ubuntu 20.04 on x86_64.

make -j8
[  2%] Built target helpcom
[  4%] Building CXX object unix/CMakeFiles/os_hc.dir/unix.cpp.o
/home/stu/projects/external/iterated-dynamics/unix/unix.cpp: In function ‘int stricmp(const char*, const char*)’:
/home/stu/projects/external/iterated-dynamics/unix/unix.cpp:68:29: error: ‘tolower’ is not a member of ‘std’
   68 |         const int c1 = std::tolower(*s1++);
      |                             ^~~~~~~
/home/stu/projects/external/iterated-dynamics/unix/unix.cpp:69:29: error: ‘tolower’ is not a member of ‘std’
   69 |         const int c2 = std::tolower(*s2++);
      |                             ^~~~~~~
/home/stu/projects/external/iterated-dynamics/unix/unix.cpp: In function ‘int strnicmp(const char*, const char*, int)’:
/home/stu/projects/external/iterated-dynamics/unix/unix.cpp:99:29: error: ‘tolower’ is not a member of ‘std’
   99 |         const int c1 = std::tolower(*s1++);
      |                             ^~~~~~~
/home/stu/projects/external/iterated-dynamics/unix/unix.cpp:100:29: error: ‘tolower’ is not a member of ‘std’
  100 |         const int c2 = std::tolower(*s2++);
      |                             ^~~~~~~
/home/stu/projects/external/iterated-dynamics/unix/unix.cpp: In function ‘char* strlwr(char*)’:
/home/stu/projects/external/iterated-dynamics/unix/unix.cpp:134:22: error: ‘tolower’ is not a member of ‘std’
  134 |         *sptr = std::tolower(*sptr);
      |                      ^~~~~~~
/home/stu/projects/external/iterated-dynamics/unix/unix.cpp: In function ‘char* strupr(char*)’:
/home/stu/projects/external/iterated-dynamics/unix/unix.cpp:158:22: error: ‘toupper’ is not a member of ‘std’; did you mean ‘tuple’?
  158 |         *sptr = std::toupper(*sptr);
      |                      ^~~~~~~
      |                      tuple
make[2]: *** [unix/CMakeFiles/os_hc.dir/build.make:63: unix/CMakeFiles/os_hc.dir/unix.cpp.o] Error 1
make[1]: *** [CMakeFiles/Makefile2:201: unix/CMakeFiles/os_hc.dir/all] Error 2
make: *** [Makefile:84: all] Error 2

LegalizeAdulthood / iterated-dynamics

Issue with toupper when compiling #41