Move entirety of llvm namespace to wpi namespace.

During shared library loading, a different libLLVM can be pulled in, causing
llvm symbols from dependent libraries to resolve to that library instead of
this one. This has been seen in the wild with the Mesa OpenGL implementation
in JavaFX applications (see wpilibsuite/shuffleboard#361).

This is clearly a very breaking change. For some level of backwards
compatibility, a namespace alias from llvm to wpi is performed in the "llvm"
headers.  Unfortunately, forward declarations of llvm classes will still break,
but compilers seem to generate clear error messages in those cases
("namespace alias 'llvm' not allowed here, assuming 'wpi'").

This change also moves all the wpiutil headers to a single "wpi" subdirectory
from the previously split "llvm", "support", "tcpsockets", and "udpsockets".
Shim headers will be added for backwards compatibility in a later commit.

wpiutil/src/main/native/cpp/llvm/raw_ostream.cpp

@@ -11,14 +11,14 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "llvm/raw_ostream.h"
-#include "llvm/SmallString.h"
-#include "llvm/SmallVector.h"
-#include "llvm/StringExtras.h"
-#include "llvm/Compiler.h"
-#include "llvm/Format.h"
-#include "llvm/MathExtras.h"
-#include "llvm/WindowsError.h"
+#include "wpi/raw_ostream.h"
+#include "wpi/SmallString.h"
+#include "wpi/SmallVector.h"
+#include "wpi/StringExtras.h"
+#include "wpi/Compiler.h"
+#include "wpi/Format.h"
+#include "wpi/MathExtras.h"
+#include "wpi/WindowsError.h"
 #include <cctype>
 #include <cerrno>
 #include <sys/stat.h>
@@ -53,7 +53,7 @@
 #include "Windows/WindowsSupport.h"
 #endif
 
-using namespace llvm;
+using namespace wpi;
 
 raw_ostream::~raw_ostream() {
   // raw_ostream's subclasses should take care to flush the buffer
@@ -657,7 +657,7 @@ size_t raw_fd_ostream::preferred_buffer_size() const {
 
 /// outs() - This returns a reference to a raw_ostream for standard output.
 /// Use it like: outs() << "foo" << "bar";
-raw_ostream &llvm::outs() {
+raw_ostream &wpi::outs() {
   // Set buffer settings to model stdout behavior.  Delete the file descriptor
   // when the program exits, forcing error detection.  This means that if you
   // ever call outs(), you can't open another raw_fd_ostream on stdout, as we'll
@@ -670,14 +670,14 @@ raw_ostream &llvm::outs() {
 
 /// errs() - This returns a reference to a raw_ostream for standard error.
 /// Use it like: errs() << "foo" << "bar";
-raw_ostream &llvm::errs() {
+raw_ostream &wpi::errs() {
   // Set standard error to be unbuffered by default.
   static raw_fd_ostream S(STDERR_FILENO, false, true);
   return S;
 }
 
 /// nulls() - This returns a reference to a raw_ostream which discards output.
-raw_ostream &llvm::nulls() {
+raw_ostream &wpi::nulls() {
   static raw_null_ostream S;
   return S;
 }