Merge bitcoin/bitcoin#24772: refactor: Use [[maybe_unused]] attribute

07ddecb refactor: Use [[maybe_unused]] attribute (Hennadii Stepanov)
55e0fc8 refactor: Drop unneeded workarounds aimed to silence unused warning (Hennadii Stepanov)

Pull request description:

  This change is required for bitcoin/bitcoin#24773 as it prevents MSVC yelling about "warning C4551: function call missing argument list".

  But it is useful by itself as it makes code more concise and readable.

ACKs for top commit:
  Empact:
    Code review ACK 07ddecb
  laanwj:
    Code review ACK 07ddecb
  vincenzopalazzo:
    ACK bitcoin/bitcoin@07ddecb
  w0xlt:
    ACK 07ddecb

Tree-SHA512: 01791855a9ba742202d5718203303af989fcb501b7cf2a24ac8d78e87487acca38f77bef264b8e27e41ad1ccf96e426725cf65bfd96ce2ac71c46b3792bed857

Author: laanwj

src/crypto/sha256.cpp

@@ -586,17 +586,9 @@ std::string SHA256AutoDetect()
     bool have_sse4 = false;
     bool have_xsave = false;
     bool have_avx = false;
-    bool have_avx2 = false;
-    bool have_x86_shani = false;
-    bool enabled_avx = false;
-
-    (void)AVXEnabled;
-    (void)have_sse4;
-    (void)have_avx;
-    (void)have_xsave;
-    (void)have_avx2;
-    (void)have_x86_shani;
-    (void)enabled_avx;
+    [[maybe_unused]] bool have_avx2 = false;
+    [[maybe_unused]] bool have_x86_shani = false;
+    [[maybe_unused]] bool enabled_avx = false;
 
     uint32_t eax, ebx, ecx, edx;
     GetCPUID(1, 0, eax, ebx, ecx, edx);
@@ -641,7 +633,7 @@ std::string SHA256AutoDetect()
         ret += ",avx2(8way)";
     }
 #endif
-#endif
+#endif // defined(USE_ASM) && defined(HAVE_GETCPUID)
 
 #if defined(ENABLE_ARM_SHANI) && !defined(BUILD_BITCOIN_INTERNAL)
     bool have_arm_shani = false;