Add support for Visual Studio 15.0 (MSVC2017)

Extend ABI by flavor and add look-up.

As with each major update, rewrite the the MSVC toolchain
autodetection.
Previously, the detection looped over the entries in "VC" registry
section and checked in the "VS" section whether a valid installation
belonged to the entry. MSVC2017 no longer has an entry in the "VC"
section.
Introduce a struct describing the installation including version
number and rewrite the loop to run over the "VS" section and retrieve
the VC path from the "VC" section only for versions <= 14.0.
Also, the various .bat files for the target architecture are
now in a single folder instead of spread around various bin/XXX
subfolders. Introduce an array of structs for the platform that
has the prefix and .bat name and uses the prefix only for
versions <= 14.0.

Task-number: QTBUG-57086
Change-Id: I947edd885c0a379f196440041c07d60cd4244d9c
Reviewed-by: Eike Ziller <eike.ziller@qt.io>
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>
Reviewed-by: David Schulz <david.schulz@qt.io>
Reviewed-by: Tobias Hunger <tobias.hunger@qt.io>

src/plugins/projectexplorer/abi.cpp

@@ -695,6 +695,8 @@ QString Abi::toString(const OSFlavor &of)
         return QLatin1String("msvc2013");
     case Abi::WindowsMsvc2015Flavor:
         return QLatin1String("msvc2015");
+    case Abi::WindowsMsvc2017Flavor:
+        return QLatin1String("msvc2017");
     case Abi::WindowsMSysFlavor:
         return QLatin1String("msys");
     case Abi::WindowsCEFlavor:

src/plugins/projectexplorer/abi.h

@@ -85,6 +85,7 @@ public:
         WindowsMsvc2012Flavor,
         WindowsMsvc2013Flavor,
         WindowsMsvc2015Flavor,
+        WindowsMsvc2017Flavor,
         WindowsMSysFlavor,
         WindowsCEFlavor,
 

src/plugins/projectexplorer/msvctoolchain.h

@@ -30,6 +30,7 @@
 #include "toolchainconfigwidget.h"
 
 QT_FORWARD_DECLARE_CLASS(QLabel)
+QT_FORWARD_DECLARE_CLASS(QVersionNumber)
 
 namespace ProjectExplorer {
 namespace Internal {
@@ -133,9 +134,8 @@ public:
     ToolChain *restore(const QVariantMap &data) override;
 
     ToolChainConfigWidget *configurationWidget(ToolChain *);
-    static QString vcVarsBatFor(const QString &basePath, MsvcToolChain::Platform platform);
-private:
-    static bool checkForVisualStudioInstallation(const QString &vsName);
+    static QString vcVarsBatFor(const QString &basePath, MsvcToolChain::Platform platform,
+                                const QVersionNumber &v);
 };
 
 // --------------------------------------------------------------------------