[ELF] - Add testcase for -debugger-tune=<value>

[grimar]

Summary

In D42733 we supported different LTO command line
options, including -debugger-tune=<value>.

Initially debugger-tune support was needed to fix PR36035.
Patch adds testcase for this option to check we
don't simply ignore it.

[ruiu]

LGTM

test/ELF/lto/debugger-tune.ll

+; REQUIRES: x86
+; RUN: llvm-as %s -o %t.o
+
+; Here we verify that -debugger-tune=<value> option is
+; handled by LLD. DWARF linkage name attributes are optional,
+; they normally present, but are missing for SCE debugger tune.
+
+; RUN: ld.lld %t.o -o %t.exe
+; RUN: llvm-dwarfdump %t.exe | FileCheck %s
+; CHECK: DW_AT_linkage_name ("name_of_foo")
+
+; RUN: ld.lld -plugin-opt=-debugger-tune=sce %t.o -o %t.exe
+; RUN: llvm-dwarfdump %t.exe | FileCheck --check-prefix=SCE %s
+; SCE-NOT: name_of_foo
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+@foo = global i32 0, align 4, !dbg !0
+
+!llvm.dbg.cu = !{!5}
+!llvm.module.flags = !{!8, !9}
+
+!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+!1 = distinct !DIGlobalVariable(name: "global_foo", linkageName: "name_of_foo", scope: !2,
+     file: !3, line: 2, type: !4, isLocal: false, isDefinition: true)
+!2 = !DINamespace(name: "test", scope: null)
+!3 = !DIFile(filename: "test.cpp", directory: "/home/tests")
+!4 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!5 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !3, producer: "clang",
+     isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !6, globals: !7)
+!6 = !{}
+!7 = !{!0}
+!8 = !{i32 2, !"Dwarf Version", i32 4}
+!9 = !{i32 2, !"Debug Info Version", i32 3}