Fix building with newer versions of Clang.

Clang has started caring that templates have C++ linkage. This just
rearranges where the extern C is specified so that the C++ decls are all
outside of the extern C block.

Issue: PLCR-546

Source/PLCrashAsyncImageList.h

@@ -29,10 +29,6 @@
 #ifndef PLCRASH_ASYNC_IMAGE_LIST_H
 #define PLCRASH_ASYNC_IMAGE_LIST_H
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #include <stdint.h>
 #include <libkern/OSAtomic.h>
 #include <stdbool.h>
@@ -48,6 +44,10 @@ extern "C" {
 #include "PLCrashAsyncLinkedList.hpp"
 #endif
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 typedef struct plcrash_async_image plcrash_async_image_t;
 
 /**

Source/PLCrashFrameWalker.h

@@ -29,10 +29,6 @@
 #ifndef PLCRASH_FRAMEWALKER_H
 #define PLCRASH_FRAMEWALKER_H
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #import <sys/ucontext.h>
 #import <pthread.h>
 
@@ -59,6 +55,10 @@ extern "C" {
 #include <mach/arm/thread_state.h>
 #endif
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 /**
  * @internal
  * @defgroup plframe_backtrace Backtrace Frame Walker