libc: add linux headers

Yeah

Signed-off-by: kaguya <vpshinomiya@protonmail.com>

ext2_root/usr/include/ifaddrs.h

@@ -0,0 +1,37 @@
+
+#ifndef  _IFADDRS_H
+#define  _IFADDRS_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include <netinet/in.h>
+#include <sys/socket.h>
+
+/* Struct definitions taken from musl */
+struct ifaddrs {
+	struct ifaddrs *ifa_next;
+	char *ifa_name;
+	unsigned ifa_flags;
+	struct sockaddr *ifa_addr;
+	struct sockaddr *ifa_netmask;
+	/* the man page (and glibc) place `ifa_broadaddr` and `ifa_dstaddr` in a union */
+	/* TODO: decide whether we should do it, too */
+	struct sockaddr *ifa_broadaddr;
+	struct sockaddr *ifa_dstaddr;
+	void *ifa_data;
+};
+
+#ifndef __MLIBC_ABI_ONLY
+
+int getifaddrs(struct ifaddrs **__ifap);
+void freeifaddrs(struct ifaddrs *__ifa);
+
+#endif /* !__MLIBC_ABI_ONLY */
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* _IFADDRS_H */