Put llvm.powi in the dev list of intrinsics.

This is used by the LLVM translator as part of:
lib/Analysis/ConstantFolding.cpp (it tries to do constant
folding for pow calls...)

Also, tweak comment about llvm.pow vs llvm.powi.  It
looks like powi is the imprecise one, not pow.

BUG=unblock DEPs roll, broken self-build.
BUG=http://code.google.com/p/nativeclient/issues/detail?id=3378
[email protected]

Review URL: https://codereview.chromium.org/14631013

Author: Jan Voung

lib/Analysis/NaCl/PNaClABIVerifyModule.cpp

@@ -174,7 +174,8 @@ bool PNaClABIVerifyModule::IsWhitelistedIntrinsic(const Function* F,
     case Intrinsic::log2: // Rounding not defined: support with fast-math?
     case Intrinsic::log10: // Rounding not defined: support with fast-math?
     case Intrinsic::nacl_target_arch: // Used by translator self-build.
-    case Intrinsic::pow: // Rounding not defined: support with fast-math?
+    case Intrinsic::pow: // Rounding is supposed to be the same as libm.
+    case Intrinsic::powi: // Rounding not defined: support with fast-math?
     case Intrinsic::prefetch: // Could ignore if target doesn't support?
     case Intrinsic::returnaddress: // Support for 0-level or not?
     case Intrinsic::sin: // Rounding not defined: support with fast-math?