CppTools: Take "-include" files into account

Fixes: QTCREATORBUG-20602
Change-Id: Ibfc518fc64ed75f93265db800558ec1d2e424bb4
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/cpptools/compileroptionsbuilder.cpp

@@ -140,6 +140,7 @@ QStringList CompilerOptionsBuilder::build(ProjectFile::Kind fileKind,
     addLanguageVersionAndExtensions();
     addMsvcExceptions();
 
+    addIncludedFiles(m_projectPart.includedFiles); // GCC adds these before precompiled headers.
     addPrecompiledHeaderOptions(usePrecompiledHeaders);
     addProjectConfigFileInclude();
 
@@ -368,6 +369,21 @@ void CompilerOptionsBuilder::addHeaderPathOptions()
     }
 }
 
+void CompilerOptionsBuilder::addIncludedFiles(const QStringList &files)
+{
+    QStringList result;
+
+    const QString includeOptionString
+            = QLatin1String(isClStyle() ? includeFileOptionCl : includeFileOptionGcc);
+    for (const QString &file : files) {
+        if (QFile::exists(file)) {
+            result += includeOptionString;
+            result += QDir::toNativeSeparators(file);
+        }
+    }
+    m_options.append(result);
+}
+
 void CompilerOptionsBuilder::addPrecompiledHeaderOptions(UsePrecompiledHeaders usePrecompiledHeaders)
 {
     for (const QString &pchFile : m_projectPart.precompiledHeaders) {
@@ -830,6 +846,12 @@ void CompilerOptionsBuilder::evaluateCompilerFlags()
             continue;
         }
 
+        // These were already parsed into ProjectPart::includedFiles.
+        if (option == includeFileOptionCl || option == includeFileOptionGcc) {
+            skipNext = true;
+            continue;
+        }
+
         if (option.startsWith("/Y", Qt::CaseSensitive)
             || (option.startsWith("/F", Qt::CaseSensitive) && option != "/F")) {
             // Precompiled header flags.