[Windows] Convert from UTF-8 to UTF-16 when writing to a Windows console

Summary:
Calling WriteConsoleW is the most reliable way to print Unicode
characters to a Windows console.

If binary data gets printed to the console, attempting to re-encode it
shouldn't be a problem, since garbage in can produce garbage out.

This breaks printing strings in the local codepage, which WriteConsoleA
knows how to handle. For example, this can happen when user source code
is encoded with the local codepage, and an LLVM tool quotes it while
emitting a caret diagnostic. This is unfortunate, but well-behaved tools
should validate that their input is UTF-8 and escape non-UTF-8
characters before sending them to raw_fd_ostream. Clang already does
this, but not all LLVM tools do this.

One drawback to the current implementation is printing a string a byte
at a time doesn't work. Consider this LLVM code:
  for (char C : MyStr) outs() << C;

Because outs() is now unbuffered, we wil try to convert each byte to
UTF-16, which will fail. However, this already didn't work, so I think
we may as well update callers that do that as we find them to print
complete portions of strings. You can see a real example of this in my
patch to SourceMgr.cpp

Fixes PR38669 and PR36267.

Reviewers: zturner, efriedma

Subscribers: llvm-commits, hiraditya

Differential Revision: https://reviews.llvm.org/D51558

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@341433 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Support/Locale.cpp

@@ -7,24 +7,11 @@ namespace sys {
 namespace locale {
 
 int columnWidth(StringRef Text) {
-#ifdef _WIN32
-  return Text.size();
-#else
   return llvm::sys::unicode::columnWidthUTF8(Text);
-#endif
 }
 
 bool isPrint(int UCS) {
-#ifdef _WIN32
-  // Restrict characters that we'll try to print to the lower part of ASCII
-  // except for the control characters (0x20 - 0x7E). In general one can not
-  // reliably output code points U+0080 and higher using narrow character C/C++
-  // output functions in Windows, because the meaning of the upper 128 codes is
-  // determined by the active code page in the console.
-  return ' ' <= UCS && UCS <= '~';
-#else
   return llvm::sys::unicode::isPrintable(UCS);
-#endif
 }
 
 } // namespace locale