Typo in hp2ps help output

As spotted by Julian Gilbey and reported at http://bugs.debian.org/710305
--show-options lists all flags. Add user documentation for #7843
Cleaning fixes, and other build system tweaks; part of #7941
Whitespace only in rts/storage/SMPClosureOps.h
Optimization for takeMVar/putMVar when MVar left empty; fixes #7923

We only need to apply the write barrier to an MVar when it acquires
a reference to live data; when the MVar is left empty in the case
of a takeMVar/putMVar, we can save a memory reference.

Patch from Edward Z. Yang.
Allow multiple C finalizers to be attached to a Weak#

The commit replaces mkWeakForeignEnv# with addCFinalizerToWeak#.
This new primop mutates an existing Weak# object and adds a new
C finalizer to it.

This change removes an invariant in MarkWeak.c, namely that the relative
order of Weak# objects in the list needs to be preserved across GC. This
makes it easier to split the list into per-generation structures.

The patch also removes a race condition between two threads calling
finalizeWeak# on the same WEAK object at that same time.
Check for a weak pointer being dead before we do any allocation for it
Maintain per-generation lists of weak pointers (#7847)
Add braces for clarity
Whitespace and braces only
Optimise lockClosure when n_capabilities == 1; fixes #693

Based on a patch from Yuras Shumovich.
Fix ghci crash when the user code closes stdin

Now that we share stdin with the program, we have to check for
handle-closed as well as EOF, as the program might have closed
stdin.
Detect linker information at runtime. Fixes Trac #6063

Previously, we did ./configure time checks to see if 'GNU ld' supported
certain options. If it does, we bake those options into the link step.
See Trac #5240.

Unfortunately, the linker we use at runtime can change for several
reasons. One is that the user specifies -pgml 'foo'. The other is if
/usr/bin/ld or whatnot changes from when GHC was built.  Those options
mentioned earlier are specific to GNU ld, but many systems support GNU
gold too. This is Trac #6063.

So we need to check at runtime what linker we're using. This is actually
a little bit complicated because we normally use the C compiler as our
linker. Windows and OS X are also special here.

Finally, this patch also unconditionally gives '--hash-size=31' and
'--reduce-memory-overheads' to the system linker if it's GNU ld. These
options have been supported for 8+ years from what I can see, and there
are probably a lot of other reasons why GHC would not work with such an
ancient binutils, all things considered.

See Note [Run-time linker info] in SysTools for details. There are
plenty of comments as well in the surrounding code.

Signed-off-by: Austin Seipp <aseipp@pobox.com>
Release note blurb for Linker fixes.

Signed-off-by: Austin Seipp <aseipp@pobox.com>
Add some missing clang bits to the build system.

Signed-off-by: Austin Seipp <aseipp@pobox.com>
Work-around clang weirdness by adding a newline.

I really wish this were a joke, but alas...

This gets me a working stage1 compiler on Linux with Clang with no
modifications. Unfortunately it won't get much farther than that for
various other reasons.

Signed-off-by: Austin Seipp <aseipp@pobox.com>
Use ideclImplicit to filter out only *implict* Prelude imports (Trac #7963)

The ideclImplicit flag didn't exist before, but it does now,
and it makes this code simpler and makes it easy to fix Trac #7963.
Emit addUsedRdrNames for the datacons in a standalone deriving (Trac #7969)
Remove redundant import, revealed by the fix to #7963
Merge remote-tracking branch 'origin/master' into data-kind-syntax-v2