cmd/ld: move instruction selection + layout into compilers, assemblers

- new object file reader/writer (liblink/objfile.c)
- remove old object file writing routines
- add pcdata iterator
- remove all trace of "line number stack" and "path fragments" from
  object files, linker (!!!)
- dwarf now writes a single "compilation unit" instead of one per package

This CL disables the check for chains of no-split functions that
could overflow the stack red zone. A future CL will attack the problem
of reenabling that check (issue 6931).

This CL is just the liblink and cmd/ld changes.
There are minor associated adjustments in CL 37030045.
Each depends on the other.

R=golang-dev, dave, iant
CC=golang-dev
https://codereview.appspot.com/39680043

1 files changed, 1 insertions, 0 deletions

diff --git a/src/liblink/asm6.c b/src/liblink/asm6.c
index 019ec0684..5ef00f849 100644
--- a/src/liblink/asm6.c
+++ b/src/liblink/asm6.c
@@ -1677,6 +1677,7 @@ span6(Link *ctxt, LSym *s)
 			sysfatal("loop");
 		}
 	} while(loop);
+	c += -c&(FuncAlign-1);
 	s->size = c;
 
 	if(0 /* debug['a'] > 1 */) {