cmd/ld: make lldb happy with Mach-O 6.out files

Apparently all the __DWARF sections need addresses
even though they are marked as "do not load from disk".
Continue the address numbering from the data segment.

With this change:

g% lldb helloworld
Current executable set to 'helloworld' (x86_64).
(lldb) b main.main
Breakpoint 1: where = helloworld`main.main + 25 at helloworld.go:12, address = 0x0000000000002019
(lldb) r
Process 68509 launched: '/Users/rsc/g/go/src/cmd/6l/helloworld' (x86_64)
1 location added to breakpoint 1
(lldb)
[KProcess 68509 stopped
* thread #1: tid = 0x8b7a27, 0x0000000000002019 helloworld`main.main + 25 at helloworld.go:12, stop reason = breakpoint 1.2
    frame #0: 0x0000000000002019 helloworld`main.main + 25 at helloworld.go:12
   9   	package main
   10
   11  	func main() {
-> 12  		print("hello, world\n")
   13  	}
(lldb) bt
* thread #1: tid = 0x8b7a27, 0x0000000000002019 helloworld`main.main + 25 at helloworld.go:12, stop reason = breakpoint 1.2
  * frame #0: 0x0000000000002019 helloworld`main.main + 25 at helloworld.go:12
(lldb) disas
helloworld`main.main at helloworld.go:11:
   0x2000:  movq   %gs:0x8a0, %rcx
   0x2009:  cmpq   (%rcx), %rsp
   0x200c:  ja     0x2015                    ; main.main + 21 at helloworld.go:11
   0x200e:  callq  0x20da0                   ; runtime.morestack00_noctxt at atomic_amd64x.c:28
   0x2013:  jmp    0x2000                    ; main.main at helloworld.go:11
   0x2015:  subq   $0x10, %rsp
-> 0x2019:  leaq   0x2c2e0, %rbx
   0x2021:  leaq   (%rsp), %rbp
   0x2025:  movq   %rbp, %rdi
   0x2028:  movq   %rbx, %rsi
   0x202b:  movsq
   0x202d:  movsq
   0x202f:  callq  0x10300                   ; runtime.printstring at compiler.go:1
   0x2034:  addq   $0x10, %rsp
   0x2038:  ret
   0x2039:  addb   %al, (%rax)
   0x203b:  addb   %al, (%rax)
   0x203d:  addb   %al, (%rax)
(lldb) quit
Quitting LLDB will kill one or more processes. Do you really want to proceed: [Y/n] y
g%

Fixes #7070.

LGTM=iant
R=golang-codereviews, iant
CC=golang-codereviews
https://golang.org/cl/93510043

src/cmd/ld/dwarf.c

@@ -2353,31 +2353,37 @@ dwarfaddmachoheaders(void)
 	ms = newMachoSeg("__DWARF", nsect);
 	ms->fileoffset = fakestart;
 	ms->filesize = abbrevo-fakestart;
+	ms->vaddr = ms->fileoffset + segdata.vaddr - segdata.fileoff;
 
 	msect = newMachoSect(ms, "__debug_abbrev", "__DWARF");
 	msect->off = abbrevo;
 	msect->size = abbrevsize;
+	msect->addr = msect->off + segdata.vaddr - segdata.fileoff;
 	ms->filesize += msect->size;
 
 	msect = newMachoSect(ms, "__debug_line", "__DWARF");
 	msect->off = lineo;
 	msect->size = linesize;
+	msect->addr = msect->off + segdata.vaddr - segdata.fileoff;
 	ms->filesize += msect->size;
 
 	msect = newMachoSect(ms, "__debug_frame", "__DWARF");
 	msect->off = frameo;
 	msect->size = framesize;
+	msect->addr = msect->off + segdata.vaddr - segdata.fileoff;
 	ms->filesize += msect->size;
 
 	msect = newMachoSect(ms, "__debug_info", "__DWARF");
 	msect->off = infoo;
 	msect->size = infosize;
+	msect->addr = msect->off + segdata.vaddr - segdata.fileoff;
 	ms->filesize += msect->size;
 
 	if (pubnamessize > 0) {
 		msect = newMachoSect(ms, "__debug_pubnames", "__DWARF");
 		msect->off = pubnameso;
 		msect->size = pubnamessize;
+		msect->addr = msect->off + segdata.vaddr - segdata.fileoff;
 		ms->filesize += msect->size;
 	}
 
@@ -2385,6 +2391,7 @@ dwarfaddmachoheaders(void)
 		msect = newMachoSect(ms, "__debug_pubtypes", "__DWARF");
 		msect->off = pubtypeso;
 		msect->size = pubtypessize;
+		msect->addr = msect->off + segdata.vaddr - segdata.fileoff;
 		ms->filesize += msect->size;
 	}
 
@@ -2392,6 +2399,7 @@ dwarfaddmachoheaders(void)
 		msect = newMachoSect(ms, "__debug_aranges", "__DWARF");
 		msect->off = arangeso;
 		msect->size = arangessize;
+		msect->addr = msect->off + segdata.vaddr - segdata.fileoff;
 		ms->filesize += msect->size;
 	}
 
@@ -2400,6 +2408,7 @@ dwarfaddmachoheaders(void)
 		msect = newMachoSect(ms, "__debug_gdb_scripts", "__DWARF");
 		msect->off = gdbscripto;
 		msect->size = gdbscriptsize;
+		msect->addr = msect->off + segdata.vaddr - segdata.fileoff;
 		ms->filesize += msect->size;
 	}
 }