[ELF] - Linkerscripts: ignore CONSTRUCTORS in output section declaration.

It is used in linux kernel script:
http://lxr.free-electrons.com/source/arch/x86/kernel/vmlinux.lds.S#L140

Though CONSTRUCTORS is ignored for ELF.

Differential revision: https://reviews.llvm.org/D28951

llvm-svn: 292777
diff --git a/lld/ELF/LinkerScript.cpp b/lld/ELF/LinkerScript.cpp
index a96a20c..ca2614d 100644
--- a/lld/ELF/LinkerScript.cpp
+++ b/lld/ELF/LinkerScript.cpp
@@ -1439,6 +1439,10 @@
     } else if (Tok == "ASSERT") {
       Cmd->Commands.emplace_back(new AssertCommand(readAssert()));
       expect(";");
+    } else if (Tok == "CONSTRUCTORS") {
+      // CONSTRUCTORS is a keyword to make the linker recognize C++ ctors/dtors
+      // by name. This is for very old file formats such as ECOFF/XCOFF.
+      // For ELF, we should ignore.
     } else if (Tok == "FILL") {
       Cmd->Filler = readFill();
     } else if (Tok == "SORT") {
diff --git a/lld/test/ELF/linkerscript/constructor.s b/lld/test/ELF/linkerscript/constructor.s
new file mode 100644
index 0000000..3fb7143
--- /dev/null
+++ b/lld/test/ELF/linkerscript/constructor.s
@@ -0,0 +1,12 @@
+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t.o
+# RUN: echo "SECTIONS { foo : { *(.foo) CONSTRUCTORS } }" > %t.script
+
+# RUN: llvm-objdump -section-headers %t1 | FileCheck %s
+# CHECK:      Sections:
+# CHECK-NEXT: Idx Name          Size
+# CHECK-NEXT:   0               00000000
+# CHECK-NEXT:   1 foo           00000001
+
+.section foo, "a"
+.byte 0