+subprocesses System can use subprocesses (for M-x shell for example). Defined by default, only MSDOS undefines it.
+USE_LISP_UNION_TYPE Define it in lisp.h to make Lisp_Object be a union type instead of the default int.
+
+** System specific macros, decribed in detail in src/s/template.h
+BSTRING
+CLASH_DETECTION
+COFF
+FIRST_PTY_LETTER
+HAVE_PTYS
+HAVE_TERMIO
+HAVE_TERMIOS
+INTERRUPT_INPUT
+MAIL_USE_FLOCK
+NARROWPROTO
+NOMULTIPLEJOBS
+SEPCHAR
+SIGTYPE
+SYSTEM_TYPE
+USE_MMAP_FOR_BUFFERS
+
+** Machine specific macros, decribed in detail in src/m/template.h
+CANNOT_DUMP
+EXPLICIT_SIGN_EXTEND
+LOAD_AVE_CVT
+LOAD_AVE_TYPE
+NO_ARG_ARRAY
+NO_REMAP
+VIRT_ADDR_VARIES
+WORDS_BIG_ENDIAN
+
+** Not used anymore by any port, can be cleaned up
+NO_SOCK_SIGIO
+
+** Misc macros
+USER_FULL_NAME If defined, overrides the default pw->pw_gecos for getting at the full user name. Only MSDOS overrides the default.