Add some ASN1_TIME related functions for the relevant PyOpenSSL patch. (#3491)

* Add ASN1_TIME related functions for the relevant PyOpenSSL patch.

* Move ASN1_TIME_check() to MACROS as the argument's constness varies between 1.0.x and 1.1.0~.
diff --git a/src/_cffi_src/openssl/asn1.py b/src/_cffi_src/openssl/asn1.py
index 4afca3d..5034c39 100644
--- a/src/_cffi_src/openssl/asn1.py
+++ b/src/_cffi_src/openssl/asn1.py
@@ -80,6 +80,7 @@
 ASN1_GENERALIZEDTIME *ASN1_TIME_to_generalizedtime(ASN1_TIME *,
                                                    ASN1_GENERALIZEDTIME **);
 ASN1_TIME *ASN1_TIME_set(ASN1_TIME *, time_t);
+int ASN1_TIME_set_string(ASN1_TIME *, const char *);
 
 /*  ASN1 UTCTIME */
 ASN1_UTCTIME *ASN1_UTCTIME_new(void);
@@ -146,6 +147,7 @@
 /* These isn't a macro the arg is const on openssl 1.0.2+ */
 int ASN1_GENERALIZEDTIME_check(ASN1_GENERALIZEDTIME *);
 int ASN1_UTCTIME_check(ASN1_UTCTIME *);
+int ASN1_TIME_check(ASN1_TIME *);
 
 /* Not a macro, const on openssl 1.0 */
 int ASN1_STRING_set_default_mask_asc(char *);