qmake: Stop using -isystem flag

This option changes the order of include paths, which can cause problems
of various kinds. See https://bugs.debian.org/958479 for an example.

The benefit of that option is minimal for what it was intended.

Pick-to: 5.15 5.12
Change-Id: I80eeabd09764df290b60bc59aeb2f90d07723608
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

2 files changed, 3 insertions, 14 deletions

diff --git a/qmake/generators/unix/unixmake2.cpp b/qmake/generators/unix/unixmake2.cpp
index 92edd1e7b6..e907114ac0 100644
--- a/qmake/generators/unix/unixmake2.cpp
+++ b/qmake/generators/unix/unixmake2.cpp
@@ -198,18 +198,13 @@ UnixMakefileGenerator::writeMakeParts(QTextStream &t)
     t << "CXXFLAGS      = " << var("QMAKE_CXXFLAGS") << " $(DEFINES)\n";
     t << "INCPATH       =";
     {
-        QString isystem = var("QMAKE_CFLAGS_ISYSTEM");
         const ProStringList &incs = project->values("INCLUDEPATH");
         for(int i = 0; i < incs.size(); ++i) {
             const ProString &inc = incs.at(i);
             if (inc.isEmpty())
                 continue;
 
-            if (!isystem.isEmpty() && isSystemInclude(inc.toQString()))
-                t << ' ' << isystem << ' ';
-            else
-                t << " -I";
-            t << escapeFilePath(inc);
+            t << " -I" << escapeFilePath(inc);
         }
     }
     if(!project->isEmpty("QMAKE_FRAMEWORKPATH_FLAGS"))
@@ -1393,8 +1388,7 @@ void UnixMakefileGenerator::init2()
     }
 
     if (include_deps && project->isActiveConfig("gcc_MD_depends")) {
-        // use -MMD if we know about -isystem too
-        ProString MD_flag(project->values("QMAKE_CFLAGS_ISYSTEM").isEmpty() ? "-MD" : "-MMD");
+        ProString MD_flag("-MD");
         project->values("QMAKE_CFLAGS") += MD_flag;
         project->values("QMAKE_CXXFLAGS") += MD_flag;
     }
diff --git a/qmake/generators/win32/mingw_make.cpp b/qmake/generators/win32/mingw_make.cpp
index 432525ffba..2ffcff9a3c 100644
--- a/qmake/generators/win32/mingw_make.cpp
+++ b/qmake/generators/win32/mingw_make.cpp
@@ -200,17 +200,12 @@ void MingwMakefileGenerator::writeIncPart(QTextStream &t)
 {
     t << "INCPATH       = ";
 
-    QString isystem = var("QMAKE_CFLAGS_ISYSTEM");
     const ProStringList &incs = project->values("INCLUDEPATH");
     for (ProStringList::ConstIterator incit = incs.begin(); incit != incs.end(); ++incit) {
         QString inc = (*incit).toQString();
         inc.replace(QRegularExpression("\\\\$"), "");
 
-        if (!isystem.isEmpty() && isSystemInclude(inc))
-            t << isystem << ' ';
-        else
-            t << "-I";
-        t << escapeFilePath(inc) << ' ';
+        t << "-I" << escapeFilePath(inc) << ' ';
     }
     t << Qt::endl;
 }