Teach raw_ostream to support hex formatting without a prefix '0x'.

Previously using format_hex() would always print a 0x prior to the
hex characters.  This allows this to be optional, so that one can
choose to print (e.g.) 255 as either 0xFF or just FF.

Differential Revision: http://reviews.llvm.org/D7151

llvm-svn: 227108
diff --git a/llvm/unittests/Support/raw_ostream_test.cpp b/llvm/unittests/Support/raw_ostream_test.cpp
index 39cfaf0..ff98602 100644
--- a/llvm/unittests/Support/raw_ostream_test.cpp
+++ b/llvm/unittests/Support/raw_ostream_test.cpp
@@ -162,6 +162,8 @@
   EXPECT_EQ("0x1",        printToString(format_hex(1, 3), 3));
   EXPECT_EQ("0x12",       printToString(format_hex(0x12, 3), 4));
   EXPECT_EQ("0x123",      printToString(format_hex(0x123, 3), 5));
+  EXPECT_EQ("FF",         printToString(format_hex_no_prefix(0xFF, 2, true), 4));
+  EXPECT_EQ("ABCD",       printToString(format_hex_no_prefix(0xABCD, 2, true), 4));
   EXPECT_EQ("0xffffffffffffffff",     
                           printToString(format_hex(UINT64_MAX, 18), 18));
   EXPECT_EQ("0x8000000000000000",