Rework the routines that convert AP[S]Int into a string. Now, instead of

returning an std::string by value, it fills in a SmallString/SmallVector
passed in.  This significantly reduces string thrashing in some cases.

More specifically, this:
 - Adds an operator<< and a print method for APInt that allows you to 
   directly send them to an ostream.
 - Reimplements APInt::toString to be much simpler and more efficient
   algorithmically in addition to not thrashing strings quite as much.

This speeds up llvm-dis on kc++ by 7%, and may also slightly speed up the
asmprinter.  This also fixes a bug I introduced into the asmwriter in a
previous patch w.r.t. alias printing.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@54873 91177308-0d34-0410-b5e6-96231b3b80d8

examples/HowToUseJIT/HowToUseJIT.cpp

@@ -107,6 +107,6 @@ int main() {
   GenericValue gv = EE->runFunction(FooF, noargs);
 
   // Import result of execution:
-  std::cout << "Result: " << gv.IntVal.toStringUnsigned(10) << "\n";
+  std::cout << "Result: " << gv.IntVal << "\n";
   return 0;
 }