curl: support embedding a CA bundle

Add the ability to embed a CA bundle into the curl binary. It is used
when no other runtime or build-time option set one.

This helps curl-for-win macOS and Linux builds to run standalone, and
also helps Windows builds to avoid picking up the CA bundle from an
arbitrary (possibly world-writable) location (though this behaviour is
not currently disablable).

Usage:
- cmake: `-DCURL_CA_EMBED=/path/to/curl-ca-bundle.crt`
- autotools: `--with-ca-embed=/path/to/curl-ca-bundle.crt`
- Makefile.mk: `CURL_CA_EMBED=/path/to/curl-ca-bundle.crt`

Also add new command-line option `--dump-ca-embed` to dump the embedded
CA bundle to standard output.

Closes #14059

src/tool_libinfo.c

@@ -124,6 +124,7 @@ static struct feature_name_presentp {
 
 static const char *fnames[sizeof(maybe_feature) / sizeof(maybe_feature[0])];
 const char * const *feature_names = fnames;
+size_t feature_count;
 
 /*
  * libcurl_info_init: retrieves runtime information about libcurl,
@@ -182,6 +183,7 @@ CURLcode get_libcurl_info(void)
           *p->feature_presentp = TRUE;
         break;
       }
+    ++feature_count;
   }
 
   return CURLE_OK;