[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

lldb/source/DataFormatters/ValueObjectPrinter.cpp

@@ -331,7 +331,7 @@ TypeSummaryImpl *ValueObjectPrinter::GetSummaryFormatter(bool null_if_omitted) {
                                  : m_valobj->GetSummaryFormat().get();
 
     if (m_options.m_omit_summary_depth > 0)
-      entry = NULL;
+      entry = nullptr;
     m_summary_formatter.first = entry;
     m_summary_formatter.second = true;
   }
@@ -415,8 +415,9 @@ bool ValueObjectPrinter::PrintValueAndSummaryIfNeeded(bool &value_printed,
       // explicitly)
       TypeSummaryImpl *entry = GetSummaryFormatter();
       if (!IsNil() && !IsUninitialized() && !m_value.empty() &&
-          (entry == NULL || (entry->DoesPrintValue(m_valobj) ||
-                             m_options.m_format != eFormatDefault) ||
+          (entry == nullptr ||
+           (entry->DoesPrintValue(m_valobj) ||
+            m_options.m_format != eFormatDefault) ||
            m_summary.empty()) &&
           !m_options.m_hide_value) {
         if (m_options.m_hide_pointer_value &&