examples: declare TU-local variables static

This fixes missing-variable-declarations warnings when building with
clang.

docs/examples/fopen.c

@@ -88,7 +88,7 @@ char *url_fgets(char *ptr, size_t size, URL_FILE *file);
 void url_rewind(URL_FILE *file);
 
 /* we use a global one for convenience */
-CURLM *multi_handle;
+static CURLM *multi_handle;
 
 /* curl calls this routine to get more data */
 static size_t write_callback(char *buffer,

docs/examples/ftpuploadfrommem.c

@@ -27,7 +27,7 @@
 #include <string.h>
 #include <curl/curl.h>
 
-const char data[]=
+static const char data[]=
   "Lorem ipsum dolor sit amet, consectetur adipiscing elit. "
   "Nam rhoncus odio id venenatis volutpat. Vestibulum dapibus "
   "bibendum ullamcorper. Maecenas finibus elit augue, vel "

docs/examples/http2-download.c

@@ -43,8 +43,8 @@
 
 #define NUM_HANDLES 1000
 
-void *curl_hnd[NUM_HANDLES];
-int num_transfers;
+static void *curl_hnd[NUM_HANDLES];
+static int num_transfers;
 
 /* a handle to number lookup, highly ineffective when we do many
    transfers... */

docs/examples/http2-upload.c

@@ -45,8 +45,8 @@
 
 #define NUM_HANDLES 1000
 
-void *curl_hnd[NUM_HANDLES];
-int num_transfers;
+static void *curl_hnd[NUM_HANDLES];
+static int num_transfers;
 
 /* a handle to number lookup, highly ineffective when we do many
    transfers... */
@@ -177,7 +177,7 @@ static size_t read_callback(void *ptr, size_t size, size_t nmemb, void *userp)
   return retcode;
 }
 
-struct input indata[NUM_HANDLES];
+static struct input indata[NUM_HANDLES];
 
 static void setup(CURL *hnd, int num, const char *upload)
 {

docs/examples/post-callback.c

@@ -28,7 +28,7 @@
 #include <string.h>
 #include <curl/curl.h>
 
-const char data[]="this is what we post to the silly web server";
+static const char data[]="this is what we post to the silly web server";
 
 struct WriteThis {
   const char *readptr;