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/leb128.cpp

@@ -0,0 +1,120 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2015-2018 FIRST. All Rights Reserved.                        */
+/* Open Source Software - may be modified and shared by FRC teams. The code   */
+/* must be accompanied by the FIRST BSD license file in the root directory of */
+/* the project.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#include "wpi/leb128.h"
+
+#include "wpi/raw_istream.h"
+
+namespace wpi {
+
+/**
+ * Get size of unsigned LEB128 data
+ * @val: value
+ *
+ * Determine the number of bytes required to encode an unsigned LEB128 datum.
+ * The algorithm is taken from Appendix C of the DWARF 3 spec. For information
+ * on the encodings refer to section "7.6 - Variable Length Data". Return
+ * the number of bytes required.
+ */
+uint64_t SizeUleb128(uint64_t val) {
+  size_t count = 0;
+  do {
+    val >>= 7;
+    ++count;
+  } while (val != 0);
+  return count;
+}
+
+/**
+ * Write unsigned LEB128 data
+ * @addr: the address where the ULEB128 data is to be stored
+ * @val: value to be stored
+ *
+ * Encode an unsigned LEB128 encoded datum. The algorithm is taken
+ * from Appendix C of the DWARF 3 spec. For information on the
+ * encodings refer to section "7.6 - Variable Length Data". Return
+ * the number of bytes written.
+ */
+uint64_t WriteUleb128(SmallVectorImpl<char>& dest, uint64_t val) {
+  size_t count = 0;
+
+  do {
+    unsigned char byte = val & 0x7f;
+    val >>= 7;
+
+    if (val != 0)
+      byte |= 0x80;  // mark this byte to show that more bytes will follow
+
+    dest.push_back(byte);
+    count++;
+  } while (val != 0);
+
+  return count;
+}
+
+/**
+ * Read unsigned LEB128 data
+ * @addr: the address where the ULEB128 data is stored
+ * @ret: address to store the result
+ *
+ * Decode an unsigned LEB128 encoded datum. The algorithm is taken
+ * from Appendix C of the DWARF 3 spec. For information on the
+ * encodings refer to section "7.6 - Variable Length Data". Return
+ * the number of bytes read.
+ */
+uint64_t ReadUleb128(const char* addr, uint64_t* ret) {
+  uint32_t result = 0;
+  int shift = 0;
+  size_t count = 0;
+
+  while (1) {
+    unsigned char byte = *reinterpret_cast<const unsigned char*>(addr);
+    addr++;
+    count++;
+
+    result |= (byte & 0x7f) << shift;
+    shift += 7;
+
+    if (!(byte & 0x80)) break;
+  }
+
+  *ret = result;
+
+  return count;
+}
+
+/**
+ * Read unsigned LEB128 data from a stream
+ * @is: the input stream where the ULEB128 data is to be read from
+ * @ret: address to store the result
+ *
+ * Decode an unsigned LEB128 encoded datum. The algorithm is taken
+ * from Appendix C of the DWARF 3 spec. For information on the
+ * encodings refer to section "7.6 - Variable Length Data". Return
+ * false on stream error, true on success.
+ */
+bool ReadUleb128(raw_istream& is, uint64_t* ret) {
+  uint32_t result = 0;
+  int shift = 0;
+
+  while (1) {
+    unsigned char byte;
+    is.read(reinterpret_cast<char*>(&byte), 1);
+    if (is.has_error()) return false;
+
+    result |= (byte & 0x7f) << shift;
+    shift += 7;
+
+    if (!(byte & 0x80)) break;
+  }
+
+  *ret = result;
+
+  return true;
+}
+
+}  // namespace wpi