Don't gc .interp section.

This change fixes a bug that was introduced by r285851.
r285851 converted .interp section as an output section to an input
section. But I forgot to make it a "Live" section, so if -gc-section
is given, it was garbage collected.

llvm-svn: 286025

lld/ELF/SyntheticSections.cpp

@@ -46,12 +46,16 @@ static ArrayRef<uint8_t> createInterp() {
 template <class ELFT>
 InterpSection<ELFT>::InterpSection()
     : InputSection<ELFT>(SHF_ALLOC, SHT_PROGBITS, 1, createInterp(),
-                         ".interp") {}
+                         ".interp") {
+  this->Live = true;
+}
 
 template <class ELFT>
 BuildIdSection<ELFT>::BuildIdSection(size_t HashSize)
     : InputSection<ELFT>(SHF_ALLOC, SHT_NOTE, 1, ArrayRef<uint8_t>(),
                          ".note.gnu.build-id") {
+  this->Live = true;
+
   Buf.resize(16 + HashSize);
   const endianness E = ELFT::TargetEndianness;
   write32<E>(Buf.data(), 4);                   // Name size

lld/test/ELF/gc-sections-synthetic.s

+# REQUIRES: x86
+
+# Linker-synthesized sections shouldn't be gc'ed.
+
+# RUN: llvm-mc -filetype=obj -triple=i686-unknown-linux %p/Inputs/shared.s -o %t.o
+# RUN: ld.lld %t2 -shared -o %t.so
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t2
+# RUN: ld.lld %t2 %t.so -build-id -dynamic-linker /foo/bar -o %t.out
+# RUN: llvm-readobj -sections %t.out | FileCheck %s
+
+# CHECK: Name: .interp
+# CHECK: Name: .note.gnu.build-id
+
+.globl _start
+_start:
+  ret