Musl fixes (#143)

* use libunwind where glibc is not available

* use sys/stat.h for struct stat definition

pclsync/ppath.h

@@ -3,6 +3,7 @@
 
 #include <fcntl.h>
 #include <stdint.h>
+#include <sys/stat.h>
 
 typedef struct {
   const char *name;

pclsync/psynclib.c

@@ -30,7 +30,11 @@
 */
 
 #include <ctype.h>
+#ifdef __GLIBC__
 #include <execinfo.h>
+#else
+#include <libunwind.h>
+#endif
 #include <pthread.h>
 #include <stddef.h>
 #include <string.h>