[ELF] - Teach LLD to strip .zdebug_* sections when --strip-debug/--strip-all is specified.

[grimar]

Summary

Currently we do not strip .zdebug_*, what looks wrong.
Also this simplifies the testcase we have for this options.

[ruiu]

LGTM

lld/trunk/ELF/InputFiles.cpp

InputSectionBase *ObjFile<ELFT>::createInputSection(const Elf_Shdr &Sec) {
   // Only GNU gold supports that. We don't. For the details about that,
   // see https://gcc.gnu.org/wiki/SplitStacks
   if (Name == ".note.GNU-split-stack") {
     error(toString(this) +
           ": object file compiled with -fsplit-stack is not supported");
     return &InputSection::Discarded;
   }
 
-  if (Config->Strip != StripPolicy::None && Name.startswith(".debug"))
+  if (Config->Strip != StripPolicy::None &&
+      (Name.startswith(".debug") || Name.startswith(".zdebug")))
     return &InputSection::Discarded;
 
   // The linkonce feature is a sort of proto-comdat. Some glibc i386 object
   // files contain definitions of symbol "__x86.get_pc_thunk.bx" in linkonce
   // sections. Drop those sections to avoid duplicate symbol errors.
   // FIXME: This is glibc PR20543, we should remove this hack once that has been
   // fixed for a while.
   if (Name.startswith(".gnu.linkonce."))

lld/trunk/test/ELF/strip-debug.s

 # REQUIRES: x86
-
-# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux -g %s -o %t
-# RUN: ld.lld %t -o %t2
-# RUN: llvm-readobj -sections -symbols %t2 | FileCheck -check-prefix=DEFAULT %s
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
 # RUN: ld.lld %t -o %t2 --strip-debug
-# RUN: llvm-readobj -sections -symbols %t2 | FileCheck -check-prefix=STRIP %s
+# RUN: llvm-readobj -sections %t2 | FileCheck %s
 # RUN: ld.lld %t -o %t2 -S
-# RUN: llvm-readobj -sections -symbols %t2 | FileCheck -check-prefix=STRIP %s
+# RUN: llvm-readobj -sections %t2 | FileCheck %s
 # RUN: ld.lld %t -o %t2 --strip-all
-# RUN: llvm-readobj -sections -symbols %t2 | FileCheck -check-prefix=STRIP %s
-
-# DEFAULT: Name: .debug_info
-# DEFAULT: Name: .debug_abbrev
-# DEFAULT: Name: .debug_aranges
-# DEFAULT: Name: .debug_line
+# RUN: llvm-readobj -sections %t2 | FileCheck %s
 
-# STRIP-NOT: Name: .debug_info
-# STRIP-NOT: Name: .debug_abbrev
-# STRIP-NOT: Name: .debug_aranges
-# STRIP-NOT: Name: .debug_line
+# CHECK-NOT: Foo
+# CHECK-NOT: Bar
 
-.globl _start
-_start:
-  ret
+.section .debug_Foo,"",@progbits
+.section .zdebug_Bar,"",@progbits