[llvm-ar] Remove unneeded std::, NFCI.

This makes it more consistent with other exit() calls in llvm-ar
(and the tools in general).

llvm-svn: 299549
diff --git a/llvm/tools/llvm-ar/llvm-ar.cpp b/llvm/tools/llvm-ar/llvm-ar.cpp
index 23e86f0..1519464 100644
--- a/llvm/tools/llvm-ar/llvm-ar.cpp
+++ b/llvm/tools/llvm-ar/llvm-ar.cpp
@@ -168,7 +168,7 @@
 show_help(const std::string &msg) {
   errs() << ToolName << ": " << msg << "\n\n";
   cl::PrintHelpMessage();
-  std::exit(1);
+  exit(1);
 }
 
 // Extract the member filename from the command line for the [relpos] argument
@@ -465,7 +465,7 @@
     return;
   for (StringRef Name : Members)
     errs() << Name << " was not found\n";
-  std::exit(1);
+  exit(1);
 }
 
 static void addMember(std::vector<NewArchiveMember> &Members,