illumos gate

Several man pages make reference to -D_REENTRANT, but several of the key ones (including Intro(3), perror(3C), and threads(5)) just say to use the "-mt" compiler option. That's a Studio compiler option, while most illumos users today are using gcc (or potentially clang). The pthread_create man page even #define's _REENTRANT directly in the source, before including pthread.h. It would be better if all these man pages included or pointed to a procedure that works for these other compilers.