qmake: Fix overlong command lines for static Qt builds on Windows

Linker response files for the MinGW and Unix makefile generators are
controlled by the variable QMAKE_LINK_OBJECT_MAX.  This variable holds a
number.  If the number of object files passed to the linker exceeds this
number, a linker response file containing object file paths is created.

This heuristic is extremely imprecise.  It doesn't take into account the
length of object file names nor the length of $$OBJECTS_DIR.

Also, when using a static Qt, a big part of the linker command line are
libraries.  A relatively small example can fail to link with "The
command line is too long" on Windows, even with the object files being
in a response file.

The MinGW makefile generator already reads the variable
QMAKE_RESPONSEFILE_THRESHOLD for compiler response files.  Re-use this
variable for the linker response file of the Unix and MinGW makefile
generators.

If QMAKE_RESPONSEFILE_THRESHOLD is set, use it to determine whether to
create a response file.  QMAKE_LINK_OBJECT_MAX is then ignored.  The
response file contains objects and libraries.

If QMAKE_RESPONSEFILE_THRESHOLD is not set, use QMAKE_LINK_OBJECT_MAX to
determine whether to create a response file.  The response file contains
only object files.

QMAKE_LINK_OBJECT_SCRIPT is used in both cases to specify a common base
name of all linker response files.

Pick-to: 6.2 6.3
Task-number: QTBUG-100559
Change-Id: I3c78354fa5ebb1a86438ec804679e0ee776c3f49
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Kai Koehne <kai.koehne@qt.io>

1 files changed, 1 insertions, 1 deletions

diff --git a/qmake/generators/unix/unixmake.h b/qmake/generators/unix/unixmake.h
index 1f32e4341f..a149005e74 100644
--- a/qmake/generators/unix/unixmake.h
+++ b/qmake/generators/unix/unixmake.h
@@ -58,7 +58,7 @@ protected:
     void writeSubTargets(QTextStream &t, QList<SubTarget*> subtargets, int flags) override;
     void writeMakeParts(QTextStream &);
     bool writeMakefile(QTextStream &) override;
-    std::pair<bool, QString> writeObjectsPart(QTextStream &, bool do_incremental);
+    bool writeObjectsPart(QTextStream &, bool do_incremental);
 private:
     void init2();
     ProStringList libdirToFlags(const ProKey &key);