cmd/ld: fix off-by-one error in DWARF .debug_line transcription

The liblink refactor changed the DWARF .debug_line flow control. The mapping was off by one pcline entry. The fix here preserves pc until it can be compared to pcline.pc.

Sample dwarfdump .debug_line output for main.main from the program in issue 7351, before liblink (correct):

0x0000003c: 00 Extended: <9> 02 DW_LNE_set_address( 0x0000000000002000 )
0x00000047: 03 DW_LNS_advance_line( 6 )
0x00000049: 01 DW_LNS_copy
            0x0000000000002000      1      7      0 is_stmt

0x0000004a: 8b address += 21,  line += 1
            0x0000000000002021      1      8      0 is_stmt

0x0000004b: 02 DW_LNS_advance_pc( 153 )
0x0000004e: 03 DW_LNS_advance_line( 1 )
0x00000050: 01 DW_LNS_copy
            0x00000000000020ba      1      9      0 is_stmt


After liblink (off by one entry):

0x00001bbf: 00 Extended: <9> 02 DW_LNE_set_address( 0x0000000000002000 )
0x00001bca: 02 DW_LNS_advance_pc( 33 )
0x00001bcc: 03 DW_LNS_advance_line( 6 )
0x00001bce: 01 DW_LNS_copy
            0x0000000000002021      1      7      0 is_stmt

0x00001bcf: 02 DW_LNS_advance_pc( 153 )
0x00001bd2: 03 DW_LNS_advance_line( 1 )
0x00001bd4: 01 DW_LNS_copy
            0x00000000000020ba      1      8      0 is_stmt

0x00001bd5: 02 DW_LNS_advance_pc( 153 )
0x00001bd8: 03 DW_LNS_advance_line( 1 )
0x00001bda: 01 DW_LNS_copy
            0x0000000000002153      1      9      0 is_stmt


After this CL (the line 9 pc offset changed due to intervening compiler changes):

0x00001d07: 00 Extended: <9> 02 DW_LNE_set_address( 0x0000000000002000 )
0x00001d12: 03 DW_LNS_advance_line( 6 )
0x00001d14: 01 DW_LNS_copy
            0x0000000000002000      1      7      0 is_stmt

0x00001d15: 8b address += 21,  line += 1
            0x0000000000002021      1      8      0 is_stmt

0x00001d16: 02 DW_LNS_advance_pc( 189 )
0x00001d19: 03 DW_LNS_advance_line( 1 )
0x00001d1b: 01 DW_LNS_copy
            0x00000000000020de      1      9      0 is_stmt


Fixes issue 7351.

LGTM=rsc
R=rsc
CC=golang-codereviews
https://codereview.appspot.com/66290043
cmd/gc: make embedded, unexported fields read-only.

Fixes issue 7363.

LGTM=gri
R=gri, rsc, bradfitz
CC=golang-codereviews
https://codereview.appspot.com/66510044
cmd/gc: explain 'nointerface' method failure

The message used to say that there was a type
mismatch, which is not necessarily true.

TBR=ken2
CC=golang-codereviews
https://codereview.appspot.com/66600044
cmd/pack: fix match

Match used len(ar.files) == 0 to mean "match everything"
but it also deleted matched things from the list, so once you
had matched everything you asked for, match returned true
for whatever was left in the archive too.

Concretely, if you have an archive containing f1, f2, then
        pack t foo.a f1
would match f1 and then, because len(ar.files) == 0 after
deleting f1 from the match list, also match f2.

Avoid the problem by recording explicitly whether match
matches everything.

LGTM=r, dsymonds
R=r, dsymonds
CC=golang-codereviews
https://codereview.appspot.com/65630046
runtime: use goc2c as much as possible

Package runtime's C functions written to be called from Go
started out written in C using carefully constructed argument
lists and the FLUSH macro to write a result back to memory.

For some functions, the appropriate parameter list ended up
being architecture-dependent due to differences in alignment,
so we added 'goc2c', which takes a .goc file containing Go func
declarations but C bodies, rewrites the Go func declaration to
equivalent C declarations for the target architecture, adds the
needed FLUSH statements, and writes out an equivalent C file.
That C file is compiled as part of package runtime.

Native Client's x86-64 support introduces the most complex
alignment rules yet, breaking many functions that could until
now be portably written in C. Using goc2c for those avoids the
breakage.

Separately, Keith's work on emitting stack information from
the C compiler would require the hand-written functions
to add #pragmas specifying how many arguments are result
parameters. Using goc2c for those avoids maintaining #pragmas.

For both reasons, use goc2c for as many Go-called C functions
as possible.

This CL is a replay of the bulk of CL 15400047 and CL 15790043,
both of which were reviewed as part of the NaCl port and are
checked in to the NaCl branch. This CL is part of bringing the
NaCl code into the main tree.

No new code here, just reformatting and occasional movement
into .h files.

LGTM=r
R=dave, alex.brainman, r
CC=golang-codereviews
https://codereview.appspot.com/65220044
runtime/debug: add SetPanicOnFault

SetPanicOnFault allows recovery from unexpected memory faults.
This can be useful if you are using a memory-mapped file
or probing the address space of the current program.

LGTM=r
R=r
CC=golang-codereviews
https://codereview.appspot.com/66590044
A+C: Apisak Darakananda (individual CLA)

Generated by addca.

R=gobot
CC=golang-codereviews
https://codereview.appspot.com/65340044
reflect: better error for walking through nil embedded struct pointer

The old error was "call of reflect.Value.Field on ptr Value".

http://play.golang.org/p/Zm-ZbQaPeR

LGTM=r
R=golang-codereviews, r
CC=golang-codereviews
https://codereview.appspot.com/67020043
A+C: Jay Weisskopf (individual CLA)

Generated by addca.

R=gobot
CC=golang-codereviews
https://codereview.appspot.com/67010044