Avoid unnecessary clock_gettime() syscalls in GC stats.

Summary: Avoid unnecessary clock_gettime() syscalls in GC stats.

Test Plan: Use strace.

Reviewers: simonmar, austin

Reviewed By: simonmar, austin

Subscribers: simonmar, relrod, carter

Differential Revision: https://phabricator.haskell.org/D39
remove SPARC related comment in PPC code generator

Summary:
PowerPC does not do delay slots and there is also no requirement
to put extra instructions between FP operations and branches.

Test Plan: None. Comment change only.

Reviewers: austin, simonmar

Reviewed By: austin, simonmar

Subscribers: simonmar, relrod, carter

Differential Revision: https://phabricator.haskell.org/D40
GHC.Conc: clarify that 'forkOn' binds to capability, not a 'CPU' or 'Task'

Summary:
Capability (HEC) can migrate to other Task (thus switch CPU)
unless capability was created as a bound haskell thread.

Task also can migrate to other CPU due to OS scheduler
(unless '-qa' RTS option is set).

Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>

Test Plan: proofread for typos

Reviewers: simonmar, austin

Reviewed By: austin

Subscribers: simonmar, relrod, carter

Differential Revision: https://phabricator.haskell.org/D52