[lldb] NFC modernize codebase with modernize-use-nullptr

Summary:
NFC = [[ https://llvm.org/docs/Lexicon.html#nfc | Non functional change ]]

This commit is the result of modernizing the LLDB codebase by using
`nullptr` instread of `0` or `NULL`. See
https://clang.llvm.org/extra/clang-tidy/checks/modernize-use-nullptr.html
for more information.

This is the command I ran and I to fix and format the code base:

```
run-clang-tidy.py \
	-header-filter='.*' \
	-checks='-*,modernize-use-nullptr' \
	-fix ~/dev/llvm-project/lldb/.* \
	-format \
	-style LLVM \
	-p ~/llvm-builds/debug-ninja-gcc
```

NOTE: There were also changes to `llvm/utils/unittest` but I did not
include them because I felt that maybe this library shall be updated in
isolation somehow.

NOTE: I know this is a rather large commit but it is a nobrainer in most
parts.

Reviewers: martong, espindola, shafik, #lldb, JDevlieghere

Reviewed By: JDevlieghere

Subscribers: arsenm, jvesely, nhaehnle, hiraditya, JDevlieghere, teemperor, rnkovacs, emaste, kubamracek, nemanjai, ki.stfu, javed.absar, arichardson, kbarton, jrtc27, MaskRay, atanasyan, dexonsmith, arphaman, jfb, jsji, jdoerfert, lldb-commits, llvm-commits

Tags: #lldb, #llvm

Differential Revision: https://reviews.llvm.org/D61847

llvm-svn: 361484
diff --git a/lldb/source/Plugins/ObjectFile/ELF/ELFHeader.cpp b/lldb/source/Plugins/ObjectFile/ELF/ELFHeader.cpp
index 7f9665a..aa987107 100644
--- a/lldb/source/Plugins/ObjectFile/ELF/ELFHeader.cpp
+++ b/lldb/source/Plugins/ObjectFile/ELF/ELFHeader.cpp
@@ -114,7 +114,7 @@
 bool ELFHeader::Parse(lldb_private::DataExtractor &data,
                       lldb::offset_t *offset) {
   // Read e_ident.  This provides byte order and address size info.
-  if (data.GetU8(offset, &e_ident, EI_NIDENT) == NULL)
+  if (data.GetU8(offset, &e_ident, EI_NIDENT) == nullptr)
     return false;
 
   const unsigned byte_size = Is32Bit() ? 4 : 8;
@@ -122,11 +122,11 @@
   data.SetAddressByteSize(byte_size);
 
   // Read e_type and e_machine.
-  if (data.GetU16(offset, &e_type, 2) == NULL)
+  if (data.GetU16(offset, &e_type, 2) == nullptr)
     return false;
 
   // Read e_version.
-  if (data.GetU32(offset, &e_version, 1) == NULL)
+  if (data.GetU32(offset, &e_version, 1) == nullptr)
     return false;
 
   // Read e_entry, e_phoff and e_shoff.
@@ -134,11 +134,11 @@
     return false;
 
   // Read e_flags.
-  if (data.GetU32(offset, &e_flags, 1) == NULL)
+  if (data.GetU32(offset, &e_flags, 1) == nullptr)
     return false;
 
   // Read e_ehsize, e_phentsize, e_phnum, e_shentsize, e_shnum and e_shstrndx.
-  if (data.GetU16(offset, &e_ehsize, 6) == NULL)
+  if (data.GetU16(offset, &e_ehsize, 6) == nullptr)
     return false;
 
   // Initialize e_phnum, e_shnum, and e_shstrndx with the values read from the
@@ -224,7 +224,7 @@
   const unsigned byte_size = data.GetAddressByteSize();
 
   // Read sh_name and sh_type.
-  if (data.GetU32(offset, &sh_name, 2) == NULL)
+  if (data.GetU32(offset, &sh_name, 2) == nullptr)
     return false;
 
   // Read sh_flags.
@@ -236,7 +236,7 @@
     return false;
 
   // Read sh_link and sh_info.
-  if (data.GetU32(offset, &sh_link, 2) == NULL)
+  if (data.GetU32(offset, &sh_link, 2) == nullptr)
     return false;
 
   // Read sh_addralign and sh_entsize.
@@ -322,7 +322,7 @@
   const bool parsing_32 = byte_size == 4;
 
   // Read st_name.
-  if (data.GetU32(offset, &st_name, 1) == NULL)
+  if (data.GetU32(offset, &st_name, 1) == nullptr)
     return false;
 
   if (parsing_32) {
@@ -331,23 +331,23 @@
       return false;
 
     // Read st_info and st_other.
-    if (data.GetU8(offset, &st_info, 2) == NULL)
+    if (data.GetU8(offset, &st_info, 2) == nullptr)
       return false;
 
     // Read st_shndx.
-    if (data.GetU16(offset, &st_shndx, 1) == NULL)
+    if (data.GetU16(offset, &st_shndx, 1) == nullptr)
       return false;
   } else {
     // Read st_info and st_other.
-    if (data.GetU8(offset, &st_info, 2) == NULL)
+    if (data.GetU8(offset, &st_info, 2) == nullptr)
       return false;
 
     // Read st_shndx.
-    if (data.GetU16(offset, &st_shndx, 1) == NULL)
+    if (data.GetU16(offset, &st_shndx, 1) == nullptr)
       return false;
 
     // Read st_value and st_size.
-    if (data.GetU64(offset, &st_value, 2) == NULL)
+    if (data.GetU64(offset, &st_value, 2) == nullptr)
       return false;
   }
   return true;
@@ -365,7 +365,7 @@
   const bool parsing_32 = byte_size == 4;
 
   // Read p_type;
-  if (data.GetU32(offset, &p_type, 1) == NULL)
+  if (data.GetU32(offset, &p_type, 1) == nullptr)
     return false;
 
   if (parsing_32) {
@@ -374,7 +374,7 @@
       return false;
 
     // Read p_flags.
-    if (data.GetU32(offset, &p_flags, 1) == NULL)
+    if (data.GetU32(offset, &p_flags, 1) == nullptr)
       return false;
 
     // Read p_align.
@@ -382,7 +382,7 @@
       return false;
   } else {
     // Read p_flags.
-    if (data.GetU32(offset, &p_flags, 1) == NULL)
+    if (data.GetU32(offset, &p_flags, 1) == nullptr)
       return false;
 
     // Read p_offset, p_vaddr, p_paddr, p_filesz, p_memsz and p_align.