Toolchains: Add C++98 as a language standard.

This was curiously missing from the CompilerFlag enum, so e.g. setting
"QMAKE_CXXFLAGS += -std=c++98" in a .pro file did not have the desired
effect on higher-level code such as the code model.

Change-Id: Ia4323b699a2ccea9d3cbde10b05affe87d955277
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@theqtcompany.com>
Reviewed-by: Tobias Hunger <tobias.hunger@theqtcompany.com>

src/plugins/cpptools/cppprojects.cpp

@@ -86,6 +86,8 @@ void ProjectPart::evaluateToolchain(const ToolChain *tc,
         languageVersion = CXX14;
     else if (flags & ToolChain::StandardCxx11)
         languageVersion = CXX11;
+    else if (flags & ToolChain::StandardCxx98)
+        languageVersion = CXX98;
     else
         languageVersion = CXX11;
 

src/plugins/projectexplorer/gcctoolchain.cpp

@@ -448,6 +448,7 @@ ToolChain::CompilerFlags GccToolChain::compilerFlags(const QStringList &cxxflags
             const QByteArray std = flag.mid(5).toLatin1();
             if (std == "c++98" || std == "c++03") {
                 flags &= ~CompilerFlags(StandardCxx11 | StandardCxx14 | StandardCxx17 | GnuExtensions);
+                flags |= StandardCxx98;
             } else if (std == "gnu++98" || std == "gnu++03") {
                 flags &= ~CompilerFlags(StandardCxx11 | StandardCxx14 | StandardCxx17);
                 flags |= GnuExtensions;

src/plugins/projectexplorer/toolchain.h

@@ -101,7 +101,8 @@ public:
         OpenMP = 0x40,
         ObjectiveC = 0x80,
         StandardCxx14 = 0x100,
-        StandardCxx17 = 0x200
+        StandardCxx17 = 0x200,
+        StandardCxx98 = 0x400,
     };
     Q_DECLARE_FLAGS(CompilerFlags, CompilerFlag)