Tweak wording in an assertion, from dawn@burble.org.

llvm-svn: 112182
diff --git a/clang/lib/Lex/Preprocessor.cpp b/clang/lib/Lex/Preprocessor.cpp
index a23290e..5160acf 100644
--- a/clang/lib/Lex/Preprocessor.cpp
+++ b/clang/lib/Lex/Preprocessor.cpp
@@ -531,7 +531,7 @@
   // Preprocess Predefines to populate the initial preprocessor state.
   llvm::MemoryBuffer *SB =
     llvm::MemoryBuffer::getMemBufferCopy(Predefines, "<built-in>");
-  assert(SB && "Cannot fail to create predefined source buffer");
+  assert(SB && "Cannot create predefined source buffer");
   FileID FID = SourceMgr.createFileIDForMemBuffer(SB);
   assert(!FID.isInvalid() && "Could not create FileID for predefines?");