Support looking up absolute symbols

The Swift stdlib uses absolute symbols in the dylib to communicate
feature flags to the process. LLDB's expression evaluator needs to be
able to find them. This wires up absolute symbols so they show up in
the symtab lookup command, which is also all that's needed for them to
be visible to the expression evaluator JIT.

rdar://85093828

Differential Revision: https://reviews.llvm.org/D113445

(cherry picked from commit c9881c7)

Author: adrian-prantl

lldb/source/Symbol/Symbol.cpp

@@ -115,7 +115,8 @@ void Symbol::Clear() {
 }
 
 bool Symbol::ValueIsAddress() const {
-  return m_addr_range.GetBaseAddress().GetSection().get() != nullptr;
+  return m_addr_range.GetBaseAddress().GetSection().get() != nullptr ||
+         m_type == eSymbolTypeAbsolute;
 }
 
 ConstString Symbol::GetDisplayName() const {

lldb/source/Symbol/Symtab.cpp

@@ -1096,6 +1096,7 @@ void Symtab::FindFunctionSymbols(ConstString name, uint32_t name_type_mask,
           case eSymbolTypeCode:
           case eSymbolTypeResolver:
           case eSymbolTypeReExported:
+          case eSymbolTypeAbsolute:
             symbol_indexes.push_back(temp_symbol_indexes[i]);
             break;
           default:

lldb/test/Shell/SymbolFile/absolute-symbol.s

@@ -0,0 +1,7 @@
+# RUN: %clang %s -g -c -o %t.o
+# RUN: %lldb -b -o 'target modules lookup -s absolute_symbol' %t.o | FileCheck %s
+# CHECK: 1 symbols match 'absolute_symbol'
+# CHECK:   Address: 0x0000000012345678 (0x0000000012345678)
+# CHECK:   Summary: 0x0000000012345678
+.globl absolute_symbol
+absolute_symbol = 0x12345678