Fix type truncation warnings

Avoid type truncation warnings from a 32-bit bot due to size_t not
being unsigned long long, by converting the variables and constants to
unsigned. This was introduced by r278338 and caused warnings here:
http://bb.pgr.jp/builders/i686-mingw32-RA-on-linux/builds/15527/steps/build_llvmclang/logs/warnings%20%287%29

llvm-svn: 278406
diff --git a/llvm/lib/LTO/LTOBackend.cpp b/llvm/lib/LTO/LTOBackend.cpp
index 5e06a06..33d4f39 100644
--- a/llvm/lib/LTO/LTOBackend.cpp
+++ b/llvm/lib/LTO/LTOBackend.cpp
@@ -46,7 +46,7 @@
   auto setHook = [&](std::string PathSuffix, ModuleHookFn &Hook) {
     // Keep track of the hook provided by the linker, which also needs to run.
     ModuleHookFn LinkerHook = Hook;
-    Hook = [=](size_t Task, Module &M) {
+    Hook = [=](unsigned Task, Module &M) {
       // If the linker's hook returned false, we need to pass that result
       // through.
       if (LinkerHook && !LinkerHook(Task, M))
@@ -115,7 +115,8 @@
       C.CodeModel, C.CGOptLevel));
 }
 
-bool opt(Config &C, TargetMachine *TM, size_t Task, Module &M, bool IsThinLto) {
+bool opt(Config &C, TargetMachine *TM, unsigned Task, Module &M,
+         bool IsThinLto) {
   M.setDataLayout(TM->createDataLayout());
 
   legacy::PassManager passes;
@@ -143,7 +144,7 @@
   return true;
 }
 
-void codegen(Config &C, TargetMachine *TM, AddStreamFn AddStream, size_t Task,
+void codegen(Config &C, TargetMachine *TM, AddStreamFn AddStream, unsigned Task,
              Module &M) {
   if (C.PreCodeGenModuleHook && !C.PreCodeGenModuleHook(Task, M))
     return;
@@ -234,8 +235,8 @@
   return Error();
 }
 
-Error lto::thinBackend(Config &C, size_t Task, AddStreamFn AddStream, Module &M,
-                       ModuleSummaryIndex &CombinedIndex,
+Error lto::thinBackend(Config &C, unsigned Task, AddStreamFn AddStream,
+                       Module &M, ModuleSummaryIndex &CombinedIndex,
                        const FunctionImporter::ImportMapTy &ImportList,
                        const GVSummaryMapTy &DefinedGlobals,
                        MapVector<StringRef, MemoryBufferRef> &ModuleMap) {