VMS Help — CRTL Feature-Test Macros, Using Faster, Inlined Put and Get Functions (Integrity servers, Alpha)
Compiling with the __UNIX_PUTC macro defined enables an
optimization that sets the following I/O functions to use faster,
inlined functions:
fgetc
fputc
putc
putchar
fgetc_unlocked
fputc_unlocked
putc_unlocked
putchar_unlocked