[libunwind] Fix a few libunwind includes

In UnwindCursor.hpp, include config.h before checking _LIBUNWIND_SUPPORT_SEH_UNWIND.

Include libunwind_ext.h for UNW_STEP_SUCCESS.

Differential Revision: https://reviews.llvm.org/D86766

NOKEYCHECK=True
GitOrigin-RevId: 6332a00d696d37942f2743851c86f1d4493968f0
diff --git a/src/UnwindCursor.hpp b/src/UnwindCursor.hpp
index e8b9556..27eca08 100644
--- a/src/UnwindCursor.hpp
+++ b/src/UnwindCursor.hpp
@@ -38,6 +38,17 @@
 #define _LIBUNWIND_CHECK_LINUX_SIGRETURN 1
 #endif
 
+#include "AddressSpace.hpp"
+#include "CompactUnwinder.hpp"
+#include "config.h"
+#include "DwarfInstructions.hpp"
+#include "EHHeaderParser.hpp"
+#include "libunwind.h"
+#include "libunwind_ext.h"
+#include "Registers.hpp"
+#include "RWMutex.hpp"
+#include "Unwind-EHABI.h"
+
 #if defined(_LIBUNWIND_SUPPORT_SEH_UNWIND)
 // Provide a definition for the DISPATCHER_CONTEXT struct for old (Win7 and
 // earlier) SDKs.
@@ -75,18 +86,6 @@
 
 #endif
 
-#include "config.h"
-
-#include "AddressSpace.hpp"
-#include "CompactUnwinder.hpp"
-#include "config.h"
-#include "DwarfInstructions.hpp"
-#include "EHHeaderParser.hpp"
-#include "libunwind.h"
-#include "Registers.hpp"
-#include "RWMutex.hpp"
-#include "Unwind-EHABI.h"
-
 namespace libunwind {
 
 #if defined(_LIBUNWIND_SUPPORT_DWARF_UNWIND)