Web: use CMake to generate precompiled headers on all platforms

"Professional CMake" book suggest the following:

"Targets should build successfully with or without compiler support for precompiled headers. It
should be considered an optimization, not a requirement. In particular, do not explicitly include a
precompile header (e.g. stdafx.h) in the source code, let CMake force-include an automatically
generated precompile header on the compiler command line instead. This is more portable across
the major compilers and is likely to be easier to maintain. It will also avoid warnings being
generated from certain code checking tools like iwyu (include what you use)."

Therefore, removed the "#include <PreCompiled.h>" from sources, also
there is no need for the "#ifdef _PreComp_" anymore

src/Mod/Web/App/AppWeb.cpp

@@ -20,11 +20,8 @@
  *                                                                         *
  ***************************************************************************/
 
-#include "PreCompiled.h"
-#ifndef _PreComp_
 #include <limits>
 #include <sstream>
-#endif
 
 #include <Base/Console.h>
 #include <Base/Interpreter.h>

src/Mod/Web/App/CMakeLists.txt

@@ -5,18 +5,11 @@ set(Web_LIBS
 
 SET(Web_SRCS
     AppWeb.cpp
-    PreCompiled.cpp
     PreCompiled.h
     Server.cpp
     Server.h
 )
 
-if(FREECAD_USE_PCH)
-    add_definitions(-D_PreComp_)
-    GET_MSVC_PRECOMPILED_SOURCE("PreCompiled.cpp" PCH_SRCS ${Web_SRCS})
-    ADD_MSVC_PRECOMPILED_HEADER(Web PreCompiled.h PreCompiled.cpp PCH_SRCS)
-endif(FREECAD_USE_PCH)
-
 add_library(Web SHARED ${Web_SRCS})
 
 target_include_directories(
@@ -32,6 +25,13 @@ target_include_directories(
     ${QtNetwork_INCLUDE_DIRS}
 )
 target_link_libraries(Web ${Web_LIBS})
+
+if(FREECAD_USE_PCH)
+    target_precompile_headers(Web PRIVATE
+            $<$<COMPILE_LANGUAGE:CXX>:"${CMAKE_CURRENT_LIST_DIR}/PreCompiled.h">
+    )
+endif(FREECAD_USE_PCH)
+
 if (FREECAD_WARN_ERROR)
     target_compile_warn_error(Web)
 endif()

src/Mod/Web/App/PreCompiled.cpp

@@ -1,23 +0,0 @@
-/***************************************************************************
- *   Copyright (c) 2014 Werner Mayer <wmayer[at]users.sourceforge.net>     *
- *                                                                         *
- *   This file is part of the FreeCAD CAx development system.              *
- *                                                                         *
- *   This library is free software; you can redistribute it and/or         *
- *   modify it under the terms of the GNU Library General Public           *
- *   License as published by the Free Software Foundation; either          *
- *   version 2 of the License, or (at your option) any later version.      *
- *                                                                         *
- *   This library  is distributed in the hope that it will be useful,      *
- *   but WITHOUT ANY WARRANTY; without even the implied warranty of        *
- *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the         *
- *   GNU Library General Public License for more details.                  *
- *                                                                         *
- *   You should have received a copy of the GNU Library General Public     *
- *   License along with this library; see the file COPYING.LIB. If not,    *
- *   write to the Free Software Foundation, Inc., 59 Temple Place,         *
- *   Suite 330, Boston, MA  02111-1307, USA                                *
- *                                                                         *
- ***************************************************************************/
-
-#include "PreCompiled.h"

src/Mod/Web/App/PreCompiled.h

@@ -25,8 +25,6 @@
 
 #include <FCConfig.h>
 
-#ifdef _PreComp_
-
 // standard
 #include <stdexcept>
 
@@ -38,6 +36,4 @@
 #include <QCoreApplication>
 #include <QTcpSocket>
 
-#endif  //_PreComp_
-
 #endif

src/Mod/Web/App/Server.cpp

@@ -20,13 +20,11 @@
  *                                                                         *
  ***************************************************************************/
 
-#include "PreCompiled.h"
-#ifndef _PreComp_
 #include <QCoreApplication>
 #include <QTcpSocket>
 #include <memory>
 #include <stdexcept>
-#endif
+
 
 #include <Base/Exception.h>
 #include <Base/Interpreter.h>