clang-tidy: C++ headers

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

src/core/Alloc.cpp

@@ -25,7 +25,7 @@
 #elif defined(HAVE_MALLOC_H)
 #include <malloc.h>
 #else
-#include <stdlib.h>
+#include <cstdlib>
 #endif
 
 #if defined(NDEBUG) && !defined(__cpp_sized_deallocation)

src/gui/Application.cpp

@@ -35,7 +35,7 @@
 #include <QStandardPaths>
 
 #if defined(Q_OS_UNIX)
-#include <signal.h>
+#include <csignal>
 #include <sys/socket.h>
 #include <unistd.h>
 #endif

src/gui/styles/base/phantomcolor.cpp

@@ -27,8 +27,8 @@
  */
 
 #include "phantomcolor.h"
+#include <cfloat>
 #include <cmath>
-#include <float.h>
 
 namespace Phantom
 {