win: Work towards getting 'minidump' to compile

minidump/minidump_context.h

Index: minidump/minidump_context.h
diff --git a/minidump/minidump_context.h b/minidump/minidump_context.h
index 9da4c44b534644653548d7f1686de1223d9cde7f..4eb3acfa3cd13aff48502cc4483e70ad6c0c41d1 100644
--- a/minidump/minidump_context.h
+++ b/minidump/minidump_context.h
@@ -17,6 +17,7 @@
 
 #include <stdint.h>
 
+#include "base/compiler_specific.h"
 #include "snapshot/cpu_context.h"
 #include "util/numeric/int128.h"
 
@@ -187,7 +188,7 @@ struct MinidumpContextX86 {
   CPUContextX86::Fxsave fxsave;
 };
 
-//! \brief x86_64-specifc flags for MinidumpContextAMD64::context_flags.
+//! \brief x86_64-specific flags for MinidumpContextAMD64::context_flags.
 enum MinidumpContextAMD64Flags : uint32_t {
   //! \brief Identifies the context structure as x86_64. This is the same as
   //!     `CONTEXT_AMD64` on Windows for this architecture.
@@ -253,7 +254,7 @@ enum MinidumpContextAMD64Flags : uint32_t {
 //!     normally alias `dr6` and `dr7`, respectively. See Intel Software
 //!     Developer’s Manual, Volume 3B: System Programming, Part 2 (253669-052),
 //!     17.2.2 “Debug Registers DR4 and DR5”.
-struct __attribute__((aligned(16))) MinidumpContextAMD64 {
+struct ALIGNAS(16) MinidumpContextAMD64 {

[Mark Mentovai, 2015/02/02 23:32:08]

Does ALIGNAS() set the packing too? I thought that you had to do both for MSVC.

[scottmg, 2015/02/03 18:12:56]

No, but the original code didn't previously. Do you think that was mistakenly?

...

Looking through winnt.h in the Windows 8.1 SDK, it only packs the x86 CONTEXT
and leaves the x64 CONTEXT as naturally packed. So I think this matches the
layout there.

[Mark Mentovai, 2015/02/03 18:26:32]

Ah, you’re right.

   //! \brief Register parameter home address.
   //!
   //! On Windows, this field may contain the “home” address (on-stack, in the