musl uses POSIX strerror_r

--- a/src/strerror.c
+++ b/src/strerror.c
@@ -26,12 +26,8 @@
 
 const char* perf_strerror_r(int errnum, char* str, size_t len)
 {
-#if ((_POSIX_C_SOURCE >= 200112L) && !_GNU_SOURCE) || defined(__FreeBSD__) || defined(__OpenBSD__) || defined(__APPLE__)
     if (strerror_r(errnum, str, len)) {
         (void)snprintf(str, len, "Error %d", errnum);
     }
     return str;
-#else
-    return strerror_r(errnum, str, len);
-#endif
 }