replace stdint.h with cstdint

The former is deprecated by C++14. The standard says they are the same:

The header defines all types and macros the same as the C standard library
header<stdint.h>.

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

src/decoder/plugins/DsdLib.hxx

@@ -24,7 +24,7 @@
 #include "input/Offset.hxx"
 #include "util/Compiler.h"
 
-#include <stdint.h>
+#include <cstdint>
 
 class TagHandler;
 class DecoderClient;

src/decoder/plugins/FfmpegIo.hxx

@@ -24,7 +24,7 @@ extern "C" {
 #include "libavformat/avio.h"
 }
 
-#include <stdint.h>
+#include <cstdint>
 
 class DecoderClient;
 class InputStream;

src/decoder/plugins/OpusHead.cxx

@@ -19,7 +19,7 @@
 
 #include "OpusHead.hxx"
 
-#include <stdint.h>
+#include <cstdint>
 
 struct OpusHead {
 	char signature[8];

src/decoder/plugins/OpusReader.hxx

@@ -23,8 +23,8 @@
 #include "util/StringView.hxx"
 
 #include <algorithm>
+#include <cstdint>
 
-#include <stdint.h>
 #include <string.h>
 
 class OpusReader {

src/decoder/plugins/OpusTags.cxx

@@ -28,7 +28,7 @@
 #include "util/NumberParser.hxx"
 #include "util/StringView.hxx"
 
-#include <stdint.h>
+#include <cstdint>
 
 gcc_pure
 static TagType