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/input/Offset.hxx

@@ -20,7 +20,7 @@
 #ifndef MPD_OFFSET_HXX
 #define MPD_OFFSET_HXX
 
-#include <stdint.h>
+#include <cstdint>
 
 /**
  * A type for absolute offsets in a file.

src/input/ThreadInputStream.hxx

@@ -27,10 +27,9 @@
 #include "util/CircularBuffer.hxx"
 
 #include <cassert>
+#include <cstdint>
 #include <exception>
 
-#include <stdint.h>
-
 /**
  * Helper class for moving InputStream implementations with blocking
  * backend library implementation to a dedicated thread.  Data is

src/input/plugins/CdioParanoiaInputPlugin.cxx

@@ -35,9 +35,9 @@
 #include "config/Block.hxx"
 
 #include <cassert>
+#include <cstdint>
 
 #include <stdio.h>
-#include <stdint.h>
 #include <string.h>
 #include <stdlib.h>