remove gcc_unused

[[maybe_unused]] (introduced in C++17) is standard C++.

https://clang.llvm.org/docs/AttributeReference.html#maybe-unused-unused
says that this is equivalent to the GNU unused attribute.

Signed-off-by: Rosen Penev <rosenp@gmail.com>

src/lib/curl/Global.cxx

@@ -108,7 +108,7 @@ CurlGlobal::CurlGlobal(EventLoop &_loop)
 }
 
 int
-CurlSocket::SocketFunction(gcc_unused CURL *easy,
+CurlSocket::SocketFunction([[maybe_unused]] CURL *easy,
 			   curl_socket_t s, int action,
 			   void *userp, void *socketp) noexcept
 {
@@ -230,7 +230,7 @@ CurlGlobal::UpdateTimeout(long timeout_ms) noexcept
 }
 
 int
-CurlGlobal::TimerFunction(gcc_unused CURLM *_multi, long timeout_ms,
+CurlGlobal::TimerFunction([[maybe_unused]] CURLM *_multi, long timeout_ms,
 			  void *userp) noexcept
 {
 	auto &global = *(CurlGlobal *)userp;

src/lib/ffmpeg/LogCallback.cxx

@@ -47,7 +47,7 @@ FfmpegImportLogLevel(int level) noexcept
 }
 
 void
-FfmpegLogCallback(gcc_unused void *ptr, int level, const char *fmt, std::va_list vl)
+FfmpegLogCallback(void *ptr, int level, const char *fmt, std::va_list vl)
 {
 	const AVClass * cls = nullptr;
 

src/lib/nfs/Connection.cxx

@@ -172,7 +172,7 @@ NfsConnection::CancellableCallback::Callback(int err, void *data) noexcept
 
 void
 NfsConnection::CancellableCallback::Callback(int err,
-					     gcc_unused struct nfs_context *nfs,
+					     [[maybe_unused]] struct nfs_context *nfs,
 					     void *data,
 					     void *private_data) noexcept
 {
@@ -551,8 +551,8 @@ NfsConnection::OnSocketReady(unsigned flags) noexcept
 }
 
 inline void
-NfsConnection::MountCallback(int status, gcc_unused nfs_context *nfs,
-			     gcc_unused void *data) noexcept
+NfsConnection::MountCallback(int status, [[maybe_unused]] nfs_context *nfs,
+			     [[maybe_unused]] void *data) noexcept
 {
 	assert(GetEventLoop().IsInside());
 	assert(context == nfs);

src/lib/smbclient/Init.cxx

@@ -27,11 +27,11 @@
 #include <string.h>
 
 static void
-mpd_smbc_get_auth_data(gcc_unused const char *srv,
-		       gcc_unused const char *shr,
-		       char *wg, gcc_unused int wglen,
-		       char *un, gcc_unused int unlen,
-		       char *pw, gcc_unused int pwlen)
+mpd_smbc_get_auth_data([[maybe_unused]] const char *srv,
+		       [[maybe_unused]] const char *shr,
+		       char *wg, [[maybe_unused]] int wglen,
+		       char *un, [[maybe_unused]] int unlen,
+		       char *pw, [[maybe_unused]] int pwlen)
 {
 	// TODO: implement
 	strcpy(wg, "WORKGROUP");

src/lib/sqlite/Util.hxx

@@ -54,7 +54,7 @@ Bind(sqlite3_stmt *stmt, unsigned i, const char *value)
 
 template<typename... Args>
 static void
-BindAll2(gcc_unused sqlite3_stmt *stmt, gcc_unused unsigned i)
+BindAll2([[maybe_unused]] sqlite3_stmt *stmt, [[maybe_unused]] unsigned i)
 {
 	assert(int(i - 1) == sqlite3_bind_parameter_count(stmt));
 }

src/lib/upnp/Action.hxx

@@ -32,7 +32,7 @@ CountNameValuePairs() noexcept
 
 template<typename... Args>
 static constexpr unsigned
-CountNameValuePairs(gcc_unused const char *name, gcc_unused const char *value,
+CountNameValuePairs([[maybe_unused]] const char *name, [[maybe_unused]] const char *value,
 		    Args... args) noexcept
 {
 	return 1 + CountNameValuePairs(args...);

src/lib/xiph/FlacIOHandle.cxx

@@ -119,7 +119,7 @@ FlacIOEof(FLAC__IOHandle handle)
 }
 
 static int
-FlacIOClose(gcc_unused FLAC__IOHandle handle)
+FlacIOClose([[maybe_unused]] FLAC__IOHandle handle)
 {
 	/* no-op because the libFLAC caller is responsible for closing
 	   the #InputStream */