Fix build on FreeBSD 10

The libc++ used by the FreeBSD toolchain on our dist builders
has some issues with vectors of move-only types. Work around
this by using an LLVM SmallVector instead.

This can be dropped when the FreeBSD toolchain is updated.

Author: nikic

llvm/tools/llvm-profdata/llvm-profdata.cpp

@@ -184,7 +184,7 @@ typedef SmallVector<WeightedFile, 5> WeightedFileVector;
 struct WriterContext {
   std::mutex Lock;
   InstrProfWriter Writer;
-  std::vector<std::pair<Error, std::string>> Errors;
+  SmallVector<std::pair<Error, std::string>, 0> Errors;
   std::mutex &ErrLock;
   SmallSet<instrprof_error, 4> &WriterErrorCodes;