Here's my (mess of a) .pro file. I thought the problem may be here.

    TEMPLATE = app

QT += qml quick

SOURCES += main.cpp \
mysteamclass.cpp

RESOURCES += qml.qrc

# Additional import path used to resolve QML modules in Qt Creator's code model
QML_IMPORT_PATH =

# Default rules for deployment.
include(deployment.pri)

DISTFILES +=

HEADERS += \
mysteamclass.h
#--------------------------------ME= C++11 AND    LIBRARIES-----------------#

CONFIG+=c++11


INCLUDEPATH += /usr/local/include
INCLUDEPATH += /usr/local/freesteam

DEPENDPATH += /usr/local/include


 LIBS += -L/usr/local/include/

# LIBS += -L/usr/local/include -lgsl

# LIBS += -L/usr/local/include -libfreesteam
 LIBS += -L/usr/local/include -lgslcblas

LIBS+= -L/usr/lib/freesteam



win32:CONFIG(release, debug|release): LIBS += -L$$PWD/../../../../usr/lib/release/ -lfreesteam
else:win32:CONFIG(debug, debug|release): LIBS += -L$$PWD/../../../../usr/lib/debug/ -lfreesteam
else:unix: LIBS += -L$$PWD/../../../../usr/lib/ -lfreesteam

INCLUDEPATH += $$PWD/../../../../usr/include
DEPENDPATH += $$PWD/../../../../usr/include

Here's some code that's close to the #include, after following the error link on QtCreator.

    /* This is here only because every header file already includes this one.
   Get the definitions of all the appropriate `__stub_FUNCTION' symbols.
   <gnu/stubs.h> contains `#define __stub_FUNCTION' when FUNCTION is a stub
   that will always return failure (and set errno to ENOSYS).  */
#include <gnu/stubs.h>


#endif  /* features.h  */

Any thoughts on how (if) I could resolve this?

EDIT: Forgot to add that I'm using Linux Mint 17.2 x64.