bug#43987: strerror return value

Patch applied in ab9c0c9ca787da60ac9b956fdbcf4c1fa68c3300. Thanks!

bug#43987: strerror return value

This is just a very minor issue. libguile contains two calls to strerror where the result is used to initialize a char *. However, according to the strerror specification, the string returned by strerror should never be changed, so I think it would be better to use const char * instead. Philipp d