smalloc headers safe for C++

teensy4/smalloc.h

 #include <stddef.h>
 #include <stdint.h>
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 struct smalloc_pool;
 
 typedef size_t (*smalloc_oom_handler)(struct smalloc_pool *, size_t);
  */
 int sm_malloc_stats(size_t *, size_t *, size_t *, int *);
 
+#ifdef __cplusplus
+} // extern "C"
+#endif
+
 #endif

teensy4/smalloc_i.h

 #include <limits.h>
 #include <errno.h>
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 struct smalloc_hdr {
 	size_t rsz; /* real allocated size with overhead (if any) */
 	size_t usz; /* exact user size as reported by s_szalloc */
 
 void *sm_realloc_pool_i(struct smalloc_pool *spool, void *p, size_t n, int nomove);
 
+#ifdef __cplusplus
+} // extern "C"
+#endif
+
 #endif