Unconditionally include BIO_set_fd and BIO_get_fd

These functions are just wrappers over BIO_ctrls, shared between the fd
and socket BIOs. Though we don't currently support one, it is
conceivable that there would be a platform with socket BIOs but not fd
BIOs. In that case, the BIO_get_fd function would still be useful to
implement SSL_get_rfd. (And someone could conceivably implement it in
another BIO.)

Bug: 629
Change-Id: I7ac3561f76af86af32d70b1c6265c4caeaecb129
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/61727
Commit-Queue: David Benjamin <davidben@google.com>
Reviewed-by: Bob Beck <bbe@google.com>

crypto/bio/fd.c

diff --git a/crypto/bio/fd.c b/crypto/bio/fd.c
index aac8bcb..c128e81 100644
--- a/crypto/bio/fd.c
+++ b/crypto/bio/fd.c
@@ -268,6 +268,8 @@
 
 const BIO_METHOD *BIO_s_fd(void) { return &methods_fdp; }
 
+#endif  // OPENSSL_NO_POSIX_IO
+
 int BIO_set_fd(BIO *bio, int fd, int close_flag) {
   return (int)BIO_int_ctrl(bio, BIO_C_SET_FD, close_flag, fd);
 }
@@ -275,5 +277,3 @@
 int BIO_get_fd(BIO *bio, int *out_fd) {
   return (int)BIO_ctrl(bio, BIO_C_GET_FD, 0, (char *) out_fd);
 }
-
-#endif  // OPENSSL_NO_POSIX_IO