[dev.link] cmd: support large function alignment

This ports CL 226997 to the dev.link branch.
- The assembler part and old object file writing are unchanged.
- Changes to cmd/link are applied to cmd/oldlink.
- Add alignment field to new object files for the new linker.

Change-Id: Id00f323ae5bdd86b2709a702ee28bcaa9ba962f8
Reviewed-on: https://go-review.googlesource.com/c/go/+/227025
Reviewed-by: Than McIntosh <thanm@google.com>

src/cmd/link/internal/ld/data.go

@@ -2256,6 +2256,10 @@ func assignAddress(ctxt *Link, sect *sym.Section, n int, s *sym.Symbol, va uint6
 		funcsize = uint64(s.Size)
 	}
 
+	if sect.Align < s.Align {
+		sect.Align = s.Align
+	}
+
 	// On ppc64x a text section should not be larger than 2^26 bytes due to the size of
 	// call target offset field in the bl instruction.  Splitting into smaller text
 	// sections smaller than this limit allows the GNU linker to modify the long calls