llvm-lto: trivial spelling changes to distinguish custom diagnostic handler and default diagnostic handler

[ygao]

Summary

Make a trivial spelling change (capitalization) to the llvm-lto tester to distinguish when a custom diagnostic handler is installed (llvm-lto -use-diagnostic-handler) and when a default handler is being used. This is split off from D14313.

llvm/trunk/test/LTO/X86/diagnostic-handler-remarks.ll

 ; RUN: llvm-as < %s >%t.bc
 ; PR21108: Diagnostic handlers get pass remarks, even if they're not enabled.
 
 ; Confirm that there are -pass-remarks.
 ; RUN: llvm-lto -pass-remarks=inline \
 ; RUN:          -exported-symbol _main -o %t.o %t.bc 2>&1 | \
 ; RUN:     FileCheck %s -allow-empty -check-prefix=REMARKS
 ; RUN: llvm-nm %t.o | FileCheck %s -check-prefix NM
 
 ; RUN: llvm-lto -pass-remarks=inline -use-diagnostic-handler \
 ; RUN:         -exported-symbol _main -o %t.o %t.bc 2>&1 | \
-; RUN:     FileCheck %s -allow-empty -check-prefix=REMARKS
+; RUN:     FileCheck %s -allow-empty -check-prefix=REMARKS_DH
 ; RUN: llvm-nm %t.o | FileCheck %s -check-prefix NM
 
 ; Confirm that -pass-remarks are not printed by default.
 ; RUN: llvm-lto \
 ; RUN:         -exported-symbol _main -o %t.o %t.bc 2>&1 | \
 ; RUN:     FileCheck %s -allow-empty
 ; RUN: llvm-nm %t.o | FileCheck %s -check-prefix NM
 
 ; RUN: llvm-lto -use-diagnostic-handler \
 ; RUN:         -exported-symbol _main -o %t.o %t.bc 2>&1 | \
 ; RUN:     FileCheck %s -allow-empty
 ; RUN: llvm-nm %t.o | FileCheck %s -check-prefix NM
 
 ; REMARKS: remark:
+; REMARKS_DH: llvm-lto: remark:
 ; CHECK-NOT: remark:
+; CHECK-NOT: llvm-lto:
 ; NM-NOT: foo
 ; NM: main
 
 target triple = "x86_64-apple-darwin"
 
 define i32 @foo() {
   ret i32 7
 }
 
 define i32 @main() {
   %i = call i32 @foo()
   ret i32 %i
 }

llvm/trunk/tools/llvm-lto/llvm-lto.cpp

 namespace {
 struct ModuleInfo {
   std::vector<bool> CanBeHidden;
 };
 }
 
 static void handleDiagnostics(lto_codegen_diagnostic_severity_t Severity,
                               const char *Msg, void *) {
+  errs() << "llvm-lto: ";
   switch (Severity) {
   case LTO_DS_NOTE:
     errs() << "note: ";
     break;
   case LTO_DS_REMARK:
     errs() << "remark: ";
     break;
   case LTO_DS_ERROR: