cmd/gc: fix race instrumentation of unaddressable arrays.

Fixes issue 4578.

R=dvyukov, golang-dev
CC=golang-dev
https://codereview.appspot.com/7005050
runtime/race: make test driver print compilation errors
Currently it silently "succeeds" saying that it run 0 tests
if there are compilations errors.
With this change it fails and outputs the compilation error.

R=golang-dev, remyoudompheng
CC=golang-dev
https://codereview.appspot.com/7002058
exp/locale/collate: include composed characters into the table. This eliminates
the need to decompose characters for the majority of cases.  This considerably
speeds up collation while increasing the table size minimally.

To detect non-normalized strings, rather than relying on exp/norm, the table
now includes CCC information. The inclusion of this information does not
increase table size.

DETAILS
 - Raw collation elements are now a struct that includes the CCC, rather
   than a slice of ints.
 - Builder now ensures that NFD and NFC counterparts are included in the table.
   This also fixes a bug for Korean which is responsible for most of the growth
   of the table size.
 - As there is no more normalization step, code should now handle both strings
   and byte slices as input. Introduced source type to facilitate this.

NOTES
 - This change does not handle normalization correctly entirely for contractions.
   This causes a few failures with the regtest. table_test.go contains a few
   uncommented tests that can be enabled once this is fixed.  The easiest is to
   fix this once we have the new norm.Iter.
 - Removed a test cases in table_test that covers cases that are now guaranteed
   to not exist.

R=rsc, mpvl
CC=golang-dev
https://codereview.appspot.com/6971044
exp/norm: changed API of Iter.
Motivations:
 - Simpler UI. Previous API proved a bit awkward for practical purposes.
 - Iter is often used in cases where one want to be able to bail out early.
   The old implementaton had too much look-ahead to be efficient.
Disadvantages:
 - ASCII performance is bad. This is unavoidable for tiny iterations.
   Example is included to show how to work around this.

Description:
Iter now iterates per boundary/segment. It returns a slice of bytes that
either points to the input bytes, the internal decomposition strings,
or the small internal buffer that each iterator has. In many cases, copying
bytes is avoided.
The method Seek was added to support jumping around the input without
having to reinitialize.

Details:
 - Table adjustments: some decompositions exist of multiple segments.
   Decompositions that are of this type are now marked so that Iter can
   handle them separately.
 - The old iterator had a different next function for different normal forms
   that was assigned to a function pointer called by Next.
   The new iterator uses this mechanism to switch between different modes
   for handling different type of input as well.  This greatly improves
   performance for Hangul and ASCII. It is also used for multi-segment
   decompositions.
 - input is now a struct of sting and []byte, instead of an interface.
   This simplifies optimizing the ASCII case.

R=rsc
CC=golang-dev
https://codereview.appspot.com/6873072
runtime: diagnose double wakeup on Note
Double wakeup is prohibited by the Note interface
and checked in lock_sema.c.

R=golang-dev, bradfitz
CC=golang-dev
https://codereview.appspot.com/6976054