build: fix Codacy/CppCheck warnings

- remove unused variables
- declare conditionally used variables conditionally
- suppress unused variable warnings in the CMake tests
- remove dead variable stores
- consistently use WIN32 macro to detect Windows

Closes https://github.com/curl/curl/pull/3739

lib/asyn-ares.c

@@ -68,7 +68,7 @@
 #include "progress.h"
 
 #  if defined(CURL_STATICLIB) && !defined(CARES_STATICLIB) && \
-     (defined(WIN32) || defined(_WIN32) || defined(__SYMBIAN32__))
+     (defined(WIN32) || defined(__SYMBIAN32__))
 #    define CARES_STATICLIB
 #  endif
 #  include <ares.h>

lib/if2ip.c

@@ -123,7 +123,9 @@ if2ip_result_t Curl_if2ip(int af, unsigned int remote_scope,
             char ipstr[64];
 #ifdef ENABLE_IPV6
             if(af == AF_INET6) {
+#ifdef HAVE_SOCKADDR_IN6_SIN6_SCOPE_ID
               unsigned int scopeid = 0;
+#endif
               unsigned int ifscope = Curl_ipv6_scope(iface->ifa_addr);
 
               if(ifscope != remote_scope) {
@@ -149,9 +151,10 @@ if2ip_result_t Curl_if2ip(int af, unsigned int remote_scope,
 
                 continue;
               }
-#endif
+
               if(scopeid)
-                msnprintf(scope, sizeof(scope), "%%%u", scopeid);
+                  msnprintf(scope, sizeof(scope), "%%%u", scopeid);
+#endif
             }
             else
 #endif

lib/md5.c

@@ -124,7 +124,7 @@ static void MD5_Final(unsigned char digest[16], MD5_CTX *ctx)
   CC_MD5_Final(digest, ctx);
 }
 
-#elif defined(_WIN32) && !defined(CURL_WINDOWS_APP)
+#elif defined(WIN32) && !defined(CURL_WINDOWS_APP)
 
 #include <wincrypt.h>
 #include "curl_memory.h"

lib/timeval.c

@@ -66,7 +66,9 @@ struct curltime Curl_now(void)
   ** in any case the time starting point does not change once that the
   ** system has started up.
   */
+#ifdef HAVE_GETTIMEOFDAY
   struct timeval now;
+#endif
   struct curltime cnow;
   struct timespec tsnow;
 

lib/version.c

@@ -31,7 +31,7 @@
 
 #ifdef USE_ARES
 #  if defined(CURL_STATICLIB) && !defined(CARES_STATICLIB) && \
-     (defined(WIN32) || defined(_WIN32) || defined(__SYMBIAN32__))
+     (defined(WIN32) || defined(__SYMBIAN32__))
 #    define CARES_STATICLIB
 #  endif
 #  include <ares.h>

lib/vtls/gskit.c

@@ -1160,7 +1160,6 @@ static CURLcode gskit_connect_common(struct connectdata *conn, int sockindex,
   struct Curl_easy *data = conn->data;
   struct ssl_connect_data *connssl = &conn->ssl[sockindex];
   long timeout_ms;
-  Qso_OverlappedIO_t cstat;
   CURLcode result = CURLE_OK;
 
   *done = connssl->state == ssl_connection_complete;