Factor out split-dwarf test in Generic/empty.ll

In llvm/test/DebugInfo/Generic/empty.ll, there are two RUN lines. The
second one use the option "-split-dwarf-file=foo.dwo"

Since darwin doesn't support split dwarf, there is an assertion when
running the test:

"Assertion failed: (Section && "Cannot switch to a null section!"),
function switchSection, file llvm/lib/MC/MCStreamer.cpp, line 1238"

While there is an XFAIL for darwin in the test, It is not a good
practice to run a test on darwin which causes an assertion. This
patch is a small refactoring of the test so that the split-dwarf test
can be it's own file with an explicit elf triple.

Differential Review: https://reviews.llvm.org/D149106

llvm/test/DebugInfo/Generic/empty.ll

@@ -1,9 +1,5 @@
 ; UNSUPPORTED: target={{.*}}-aix{{.*}}
 ; RUN: %llc_dwarf < %s -filetype=obj | llvm-dwarfdump -v - | FileCheck %s
-; RUN: %llc_dwarf -split-dwarf-file=foo.dwo < %s -filetype=obj | llvm-dwarfdump -v - | FileCheck --check-prefix=FISSION %s
-
-; darwin has a workaround for a linker bug so it always emits one line table entry
-; XFAIL: target={{.*}}-darwin{{.*}}
 
 ; Expect no line table entry since there are no functions and file references in this compile unit
 ; CHECK: .debug_line contents:
@@ -14,11 +10,6 @@
 ; CHECK-NOT: .debug_pubnames contents:
 ; CHECK: contents:
 
-; Don't emit DW_AT_addr_base when there are no addresses.
-; Also don't emit a split line table when there are no type units.
-; FISSION-NOT: DW_AT_GNU_addr_base [DW_FORM_sec_offset]
-; FISSION-NOT: .debug_line.dwo contents:
-
 !llvm.dbg.cu = !{!0}
 !llvm.module.flags = !{!5}
 

llvm/test/DebugInfo/X86/empty-split-dwarf.ll

@@ -0,0 +1,18 @@
+; UNSUPPORTED: target={{.*}}-aix{{.*}}
+; RUN: %llc_dwarf -split-dwarf-file=foo.dwo < %s -filetype=obj --mtriple=x86_64-unknown-linux-elf | llvm-dwarfdump -v - | FileCheck --check-prefix=FISSION %s
+
+; Don't emit DW_AT_addr_base when there are no addresses.
+; Also don't emit a split line table when there are no type units.
+; FISSION-NOT: DW_AT_GNU_addr_base [DW_FORM_sec_offset]
+; FISSION-NOT: .debug_line.dwo contents:
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!5}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, producer: "clang version 3.1 (trunk 143523)", isOptimized: true, emissionKind: FullDebug, file: !4, enums: !2, retainedTypes: !6, globals: !2)
+!2 = !{}
+!3 = !DIFile(filename: "empty.c", directory: "/home/nlewycky")
+!4 = !DIFile(filename: "empty.c", directory: "/home/nlewycky")
+!5 = !{i32 1, !"Debug Info Version", i32 3}
+!6 = !{!7}
+!7 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)