Linker script: Fix bug with several .bss

When final image has several .bss sections, lld fails
because second .bss always has zero VA. This causes 
link error "Not enough space for ELF and program headers"

llvm-svn: 282067

lld/ELF/LinkerScript.cpp

@@ -453,10 +453,11 @@ void LinkerScript<ELFT>::assignOffsets(OutputSectionCommand *Cmd) {
     process(**I);
   flush();
   for (OutputSectionBase<ELFT> *Base : Sections) {
-    if (!AlreadyOutputOS.insert(Base).second)
+    if (AlreadyOutputOS.count(Base))
       continue;
     switchTo(Base);
     Dot += CurOutSec->getSize();
+    flush();
   }
   std::for_each(E, Cmd->Commands.end(),
                 [this](std::unique_ptr<BaseCommand> &B) { process(*B.get()); });

lld/test/ELF/linkerscript/double-bss.s

@@ -0,0 +1,16 @@
+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
+# RUN: echo "SECTIONS { .text : { *(.text*) } }" > %t.script
+# RUN: ld.lld -o %t1 --script %t.script %t
+# RUN: llvm-objdump -section-headers %t1 | FileCheck %s
+# CHECK:      .bss          00000004 0000000000000122 BSS
+# CHECK-NEXT: .bss          00000100 0000000000000128 BSS
+
+.globl _start
+_start:
+  jmp _start
+
+.bss
+.zero 4
+
+.comm q,128,8