Documented PCH support

Added PCH support to benchmark

Author: nmoreaud

README.md

@@ -20,6 +20,7 @@ There are two optimization levels for moc objects :
 - group every QObject classes (headers) into a single header, then call moc on this file. (`MOC_LVL_2`, even faster)
 
 QMake-unity provides good integration with Qt 5 tooling system (qmake, moc, qt-creator) and with MSBuild.
+It is compatible with precompiled headers (PCH).
 
 Here are general articles if you want to understand how it works :
 - [Jumbo, A unity build system for Chromium](https://bit.ly/jumbo-blinkon9)
@@ -222,14 +223,21 @@ It has been run on a Windows 10 laptop powered by an i5 8250u.
 
 ### [QupZilla](https://github.com/QupZilla/qupzilla) built with `MSVC`
 
-| Project part | QMake-unity  | Time             |
-| ------------ | ------------ | ---------------- |
-| lib          | not enabled  | 3m14             |
-| lib          | MOC_LVL_1    | 52s (73% faster) |
-| lib          | MOC_LVL_2    | 26s (87% faster) |
-| plugins      | not enabled  | 1m15             |
-| plugins      | MOC_LVL_1    | 27s (64% faster) |
-| plugins      | MOC_LVL_2    | 22s (71% faster) |
+PCH raw = 59s
+PCH + MOC_LVL_1 = 35s
+PCH + MOC_LVL_2 = 19s
+
+| Project part | QMake-unity  | PreCompiledHeader (PCH) | Time             |
+| ------------ | ------------ | ----------------------- | ---------------- |
+| lib          | not enabled  | not enabled             | 3m14             |
+| lib          | MOC_LVL_1    | not enabled             | 52s (73% faster) |
+| lib          | MOC_LVL_2    | not enabled             | 26s (87% faster) |
+| lib          | not enabled  | enabled                 | 59s (70% faster) |
+| lib          | MOC_LVL_1    | enabled                 | 35s (82% faster) |
+| lib          | MOC_LVL_2    | enabled                 | 15s (92% faster) |
+| plugins      | not enabled  | not enabled             | 1m15             |
+| plugins      | MOC_LVL_1    | not enabled             | 27s (64% faster) |
+| plugins      | MOC_LVL_2    | not enabled             | 22s (71% faster) |
 
 ### [QtXlsxWriter](https://github.com/dbzhang800/QtXlsxWriter) built with `MinGW`
 | QMake-unity  | Time             |
@@ -252,9 +260,9 @@ It has been run on a Windows 10 laptop powered by an i5 8250u.
 ## What else can I do to speedup my build
 
 **Pure C++ techniques :**
+- Use precompiled headers (PCH) : useful for big executables/libraries
 - Forward declare headers (incremental build)
 - Write less templates
-- Use precompiled headers (PCH)
 
 **Qt :**
 - If you build in VisualStudio, install Qt Visual Studio Tools <= 2.2; which now supports parallel calls of moc.

test/qupzilla-master/src/lib/lib.pro

@@ -502,6 +502,9 @@ message(===========================================)
 message( Using following defines:)
 message(  $$DEFINES)
 
+PRECOMPILED_HEADER = pch.h
+CONFIG += precompile_header
+
 UNITY_BUILD = 1
 UNITY_MOC_MODE = MOC_LVL_2
 include(../../../../qmakeUnity/qmake_unity.pri)

test/qupzilla-master/src/lib/pch.h

@@ -0,0 +1,66 @@
+#include <QAction>
+#include <QApplication>
+#include <QBuffer>
+#include <QByteArray>
+#include <QCheckBox>
+#include <QClipboard>
+#include <QColor>
+#include <QComboBox>
+#include <QDateTime>
+#include <QDebug>
+#include <QDialog>
+#include <QDir>
+#include <QDrag>
+#include <QFile>
+#include <QFlags>
+#include <QFrame>
+#include <QHBoxLayout>
+#include <QHash>
+#include <QHeaderView>
+#include <QIcon>
+#include <QJsonArray>
+#include <QJsonDocument>
+#include <QJsonObject>
+#include <QJsonValue>
+#include <QLabel>
+#include <QLineEdit>
+#include <QList>
+#include <QMap>
+#include <QMenu>
+#include <QMessageBox>
+#include <QMetatype>
+#include <QMimeData>
+#include <QMouseEvent>
+#include <QPainter>
+#include <QPalette>
+#include <QPixmap>
+#include <QPointer>
+#include <QProcess>
+#include <QPushButton>
+#include <QRadioButton>
+#include <QScrollBar>
+#include <QSpacerItem>
+#include <QSslCertificate>
+#include <QStackedLayout>
+#include <QStackedWidget>
+#include <QStringList>
+#include <QStyle>
+#include <QSysInfo>
+#include <QTabWidget>
+#include <QTemporaryFile>
+#include <QTextDocument>
+#include <QTimer>
+#include <QToolButton>
+#include <QToolTip>
+#include <QUrl>
+#include <QUrlQuery>
+#include <QVBoxLayout>
+#include <QVariant>
+#include <QVector>
+#include <QWebEngineContextMenuData>
+#include <QWebEngineHistory>
+#include <QWebEnginePage>
+#include <QWidget>
+//#include <QPrintDialog>
+//#include <QPrinter>
+//#include <QQuickWidget> pb avec macro "interface"