The 'X' printf type has a valid alternative form. Fixes PR8641.

llvm-svn: 119946
diff --git a/clang/lib/Analysis/PrintfFormatString.cpp b/clang/lib/Analysis/PrintfFormatString.cpp
index 57399d8..8867101 100644
--- a/clang/lib/Analysis/PrintfFormatString.cpp
+++ b/clang/lib/Analysis/PrintfFormatString.cpp
@@ -501,10 +501,11 @@
   if (!HasAlternativeForm)
     return true;
 
-  // Alternate form flag only valid with the oxaAeEfFgG conversions
+  // Alternate form flag only valid with the oxXaAeEfFgG conversions
   switch (CS.getKind()) {
   case ConversionSpecifier::oArg:
   case ConversionSpecifier::xArg:
+  case ConversionSpecifier::XArg:
   case ConversionSpecifier::aArg:
   case ConversionSpecifier::AArg:
   case ConversionSpecifier::eArg: