Move `extern "C" specifications for C++ to where they are needed

This should fix errors when compiling C++ code with modules enabled on clang.

include/jemalloc/jemalloc.sh

@@ -6,9 +6,6 @@ cat <<EOF
 #ifndef JEMALLOC_H_
 #define JEMALLOC_H_
 #pragma GCC system_header
-#ifdef __cplusplus
-extern "C" {
-#endif
 
 EOF
 
@@ -21,8 +18,5 @@ for hdr in jemalloc_defs.h jemalloc_rename.h jemalloc_macros.h \
 done
 
 cat <<EOF
-#ifdef __cplusplus
-}
-#endif
 #endif /* JEMALLOC_H_ */
 EOF

include/jemalloc/jemalloc_protos.h.in

@@ -3,6 +3,10 @@
  * of namespace management, and should be omitted in application code unless
  * JEMALLOC_NO_DEMANGLE is defined (see jemalloc_mangle@install_suffix@.h).
  */
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 extern JEMALLOC_EXPORT const char	*@je_@malloc_conf;
 extern JEMALLOC_EXPORT const char	*@je_@malloc_conf_2_conf_harder;
 extern JEMALLOC_EXPORT void		(*@je_@malloc_message)(void *cbopaque,
@@ -79,3 +83,7 @@ JEMALLOC_EXPORT JEMALLOC_ALLOCATOR JEMALLOC_RESTRICT_RETURN
     void JEMALLOC_SYS_NOTHROW	*@je_@pvalloc(size_t size) JEMALLOC_CXX_THROW
     JEMALLOC_ATTR(malloc);
 #endif
+
+#ifdef __cplusplus
+}
+#endif

include/jemalloc/jemalloc_typedefs.h.in

@@ -1,3 +1,7 @@
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 typedef struct extent_hooks_s extent_hooks_t;
 
 /*
@@ -75,3 +79,7 @@ struct extent_hooks_s {
 	extent_split_t		*split;
 	extent_merge_t		*merge;
 };
+
+#ifdef __cplusplus
+}
+#endif