replace assert.h with cassert

The former was deprecated with C++14.

According to the C++11 and C++17 standards, both files are identical.

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

src/system/EventFD.cxx

@@ -31,7 +31,8 @@
 #include "system/Error.hxx"
 #include "util/Compiler.h"
 
-#include <assert.h>
+#include <cassert>
+
 #include <sys/eventfd.h>
 
 EventFD::EventFD()

src/system/EventPipe.cxx

@@ -22,7 +22,8 @@
 #include "system/Error.hxx"
 #include "util/Compiler.h"
 
-#include <assert.h>
+#include <cassert>
+
 #include <unistd.h>
 
 #ifdef _WIN32

src/system/FileDescriptor.cxx

@@ -30,7 +30,8 @@
 #include "FileDescriptor.hxx"
 #include "system/Error.hxx"
 
-#include <assert.h>
+#include <cassert>
+
 #include <stdint.h>
 #include <sys/stat.h>
 #include <fcntl.h>

src/system/SignalFD.cxx

@@ -30,7 +30,8 @@
 #include "SignalFD.hxx"
 #include "Error.hxx"
 
-#include <assert.h>
+#include <cassert>
+
 #include <sys/signalfd.h>
 
 void

src/system/UniqueFileDescriptor.hxx

@@ -32,10 +32,9 @@
 
 #include "FileDescriptor.hxx"
 
+#include <cassert>
 #include <utility>
 
-#include <assert.h>
-
 /**
  * An OO wrapper for a UNIX file descriptor.
  */