Don't flush the raw_ostream between each MachineFunction. These flush

calls were originally put in place because errs() at one time was
not unbuffered, and these print routines are commonly used with errs()
for debugging. However, errs() is now properly unbuffered, so the
flush calls are no longer needed. This significantly reduces the
number of write(2) calls for regular asm printing when there are many
small functions.

llvm-svn: 78137