[lldb] Specify unsigned underlying type for an enumeration explicitly

The enumeration EntryType is used as a bit field of DebugMacroEntry:
```
  EntryType m_type : 3
```

Since underlying type of enumeration is implementation-dependent, a signed integer is
converted to the 3-bit value by some compilers (MSVC).

That's why a DebugMacroEntry instance that was created with EntryType value > 3 (END_FILE or INDIRECT)
contains incorrect negative value in its m_type data-member.

lldb/include/lldb/Symbol/DebugMacros.h

@@ -23,7 +23,9 @@ typedef std::shared_ptr<DebugMacros> DebugMacrosSP;
 
 class DebugMacroEntry {
 public:
-  enum EntryType { INVALID, DEFINE, UNDEF, START_FILE, END_FILE, INDIRECT };
+  enum EntryType : uint32_t {
+      INVALID, DEFINE, UNDEF, START_FILE, END_FILE, INDIRECT
+  };
 
 public:
   static DebugMacroEntry CreateDefineEntry(uint32_t line, const char *str);