Add offsetof support to expression evaluator.

Summary:
We currently don't support offsetof in the expression evaluator as it is implemented as a macro
(which then calls __builtin_offsetof) in stddef.h. The best solution would be to include that
header (or even better, import Clang's builtin module), but header-parsing and
(cross-platform) importing modules is not ready yet.

Until we get this working with modules I would say we add the macro to our existing macro list
as we already do with other macros from stddef.h/stdint.h. We should be able to drop all of them
once we can import the relevant modules by default.

rdar://26040641

Reviewers: shafik, davide

Reviewed By: davide

Subscribers: clayborg, lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D64917

llvm-svn: 366476
diff --git a/lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionSourceCode.cpp b/lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionSourceCode.cpp
index f513b1e..88cfe5f 100644
--- a/lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionSourceCode.cpp
+++ b/lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionSourceCode.cpp
@@ -30,6 +30,9 @@
 using namespace lldb_private;
 
 const char *ClangExpressionSourceCode::g_expression_prefix = R"(
+#ifndef offsetof
+#define offsetof(t, d) __builtin_offsetof(t, d)
+#endif
 #ifndef NULL
 #define NULL (__null)
 #endif