musl: hostname-util: introduce LINUX_HOST_NAME_MAX

glibc defines HOST_NAME_MAX as 64 and our code rely on that, but musl
defines the constant as 255. Let's provide our own definition for the
maximum length.

src/basic/hostname-util.h

@@ -4,6 +4,9 @@
 #include "basic-forward.h"
 #include "strv.h"
 
+/* HOST_NAME_MAX should be 64 on linux, but musl uses the one by POSIX (255). */
+#define LINUX_HOST_NAME_MAX CONST_MIN((size_t) HOST_NAME_MAX, (size_t) 64)
+
 char* get_default_hostname_raw(void);
 
 bool valid_ldh_char(char c) _const_;