lavf/tls_securetransport: build on iOS

This works as expected on iOS, except for the ca_file feature which
is disabled because SecItemImport is not available.
Signed-off-by: Aman Gupta <aman@tmm1.net>

configure

@@ -2035,6 +2035,7 @@ SYSTEM_FUNCS="
     posix_memalign
     pthread_cancel
     sched_getaffinity
+    SecItemImport
     SetConsoleTextAttribute
     SetConsoleCtrlHandler
     setmode
@@ -6032,9 +6033,12 @@ fi
 
 enabled securetransport &&
     check_func SecIdentityCreate "-Wl,-framework,CoreFoundation -Wl,-framework,Security" &&
-    check_lib securetransport "Security/SecureTransport.h Security/Security.h" "SSLCreateContext SecItemImport" "-Wl,-framework,CoreFoundation -Wl,-framework,Security" ||
+    check_lib securetransport "Security/SecureTransport.h Security/Security.h" "SSLCreateContext" "-Wl,-framework,CoreFoundation -Wl,-framework,Security" ||
         disable securetransport
 
+enabled securetransport &&
+    check_func SecItemImport "-Wl,-framework,CoreFoundation -Wl,-framework,Security"
+
 enabled schannel &&
     check_func_headers "windows.h security.h" InitializeSecurityContext -DSECURITY_WIN32 -lsecur32 &&
     check_cpp_condition winerror.h "defined(SEC_I_CONTEXT_EXPIRED)" &&

libavformat/tls_securetransport.c

@@ -69,6 +69,9 @@ static int print_tls_error(URLContext *h, int ret)
 
 static int import_pem(URLContext *h, char *path, CFArrayRef *array)
 {
+#if !HAVE_SECITEMIMPORT
+    return AVERROR_PATCHWELCOME;
+#else
     AVIOContext *s = NULL;
     CFDataRef data = NULL;
     int64_t ret = 0;
@@ -124,6 +127,7 @@ end:
     if (s)
         avio_close(s);
     return ret;
+#endif
 }
 
 static int load_ca(URLContext *h)