[LIT] Enable testing of LLVM gold plugin on Mac OS X

[tejohnson]

LGTM

test/lit.cfg.py

 # Some tests are "generic" and require a valid default triple
 if config.target_triple:
     config.available_features.add('default_triple')
 
 import subprocess
 
 
 def have_ld_plugin_support():
-    if not os.path.exists(os.path.join(config.llvm_shlib_dir, 'LLVMgold.so')):
+    if not os.path.exists(os.path.join(config.llvm_shlib_dir, 'LLVMgold' + config.llvm_shlib_ext)):
         return False
 
     ld_cmd = subprocess.Popen(
         [config.gold_executable, '--help'], stdout=subprocess.PIPE, env={'LANG': 'C'})
     ld_out = ld_cmd.stdout.read().decode()
     ld_cmd.wait()
 
     if not '-plugin' in ld_out:

test/tools/gold/X86/Inputs/common.ll

 target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
 
 @a = common global i32 0, align 4

test/tools/gold/X86/Inputs/common2.ll

 target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
 
 @a = common global i8 0, align 16

test/tools/gold/X86/Inputs/common3.ll

 target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
 
 @a = common global i8 0, align 1

test/tools/gold/X86/Inputs/drop-linkage.ll

 target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
 
 $foo = comdat any
 define linkonce void @foo() comdat {
   ret void
 }
 
 define void @bar() {
   call void @foo()
   ret void
 }

test/tools/gold/X86/common.ll

 ; RUN: llvm-as %s -o %t1.o
 ; RUN: llvm-as %p/Inputs/common.ll -o %t2.o
 ; RUN: llvm-as %p/Inputs/common2.ll -o %t2b.o
 ; RUN: llvm-as %p/Inputs/common3.ll -o %t2c.o
 
 target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
 
 @a = common global i16 0, align 8
 
 ; RUN: %gold -plugin %llvmshlibdir/LLVMgold%shlibext \
 ; RUN:    --plugin-opt=emit-llvm \
 ; RUN:    -shared %t1.o %t2.o -o %t3.o
 ; RUN: llvm-dis %t3.o -o - | FileCheck %s --check-prefix=A
 

test/tools/gold/X86/drop-linkage.ll

 ; RUN: llc %s -o %t.s
-; RUN: llvm-mc %t.s -o %t.o -filetype=obj
+; RUN: llvm-mc %t.s -o %t.o -filetype=obj -triple=x86_64-unknown-linux-gnu
 ; RUN: llvm-as %p/Inputs/drop-linkage.ll -o %t2.o
 
 ; RUN: %gold -plugin %llvmshlibdir/LLVMgold%shlibext \
 ; RUN:    --plugin-opt=emit-llvm \
 ; RUN:    -shared %t.o %t2.o -o %t3.o
 ; RUN: llvm-dis %t3.o -o - | FileCheck %s
 
 target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
 
 define void @foo() {
   ret void
 }
 
 ; CHECK: declare void @foo()

test/tools/gold/X86/thinlto_archive.ll

 ; Generate summary sections
 ; RUN: opt -module-summary %s -o %t.o
 ; RUN: opt -module-summary %p/Inputs/thinlto_archive1.ll -o %t2.o
 ; RUN: opt -module-summary %p/Inputs/thinlto_archive2.ll -o %t3.o
 
 ; Generate the static library
-; RUN: llvm-ar r %t.a %t2.o %t3.o
+; RUN: llvm-ar -format=gnu r %t.a %t2.o %t3.o
 
 ; Test importing from archive library via gold, using jobs=1 to ensure
 ; output messages are not interleaved.
 ; RUN: %gold -plugin %llvmshlibdir/LLVMgold%shlibext \
 ; RUN:    -m elf_x86_64 \
 ; RUN:    --plugin-opt=thinlto \
 ; RUN:    --plugin-opt=-print-imports \
 ; RUN:    --plugin-opt=jobs=1 \