add legacy euidaccess function and eaccess alias for it

this is mainly for ABI compat purposes.

src/legacy/euidaccess.c

+#include <unistd.h>
+#include <fcntl.h>
+#include <errno.h>
+#include "syscall.h"
+#include "libc.h"
+
+int euidaccess(const char *filename, int amode)
+{
+	int ret = __syscall(SYS_faccessat, AT_FDCWD, filename, amode, AT_EACCESS);
+	if (ret != -ENOSYS) return __syscall_ret(ret);
+
+	if (getuid() == geteuid() && getgid() == getegid())
+		return syscall(SYS_access, filename, amode);
+
+	return __syscall_ret(-ENOSYS);
+}
+
+weak_alias(euidaccess, eaccess);