Corrected some comments that were using C++-style instead of C-style 


include/my_sys.h:
  Portability fix: define alloca as a compiler builtin on systems that have
  gcc but no alloca.h (e.g. some IBM AIX flavors), use "#pragma alloca" for
  IBMs compiler (xlc)
mysys/my_getopt.c:
  Replace C++-style comments with C-style comments
strings/ctype-latin1_de.c:
  Replace C++-style comments with C-style comments
strings/ctype-tis620.c:
  Replace C++-style comments with C-style comments