lib: Fix environ on MacOS

On macOS, environ is not declared. Use the workaround suggested here:
https://www.gnu.org/software/gnulib/manual/html_node/environ.html

Signed-off-by: Antonio Caggiano <quic_acaggian@quicinc.com>

lib/guestfs-internal.h

@@ -26,6 +26,11 @@
 #ifndef GUESTFS_INTERNAL_H_
 #define GUESTFS_INTERNAL_H_
 
+#ifdef __APPLE__
+#include <crt_externs.h>
+#define environ (*_NSGetEnviron())
+#endif // __APPLE__
+
 #include <stdbool.h>
 #include <assert.h>
 

lib/handle.c

@@ -27,6 +27,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <libintl.h>
+#include <errno.h>
 
 #include <libxml/parser.h>
 #include <libxml/xmlversion.h>