Fix file descriptor leak in the perf event counter

We opened the counter at every start(), even if we had already started
before. Some of the benchlib's options caused it to start() and stop()
over and over again, like -minimumvalue and -minimumtotal, which could
leak to fd exhaustion (EMFILE).

Change-Id: Ifeb7cca65c758877be600dc22928bea74f499934
Reviewed-by: Robin Burchell <robin+qt@viroteck.net>
Reviewed-by: Jason McDonald <macadder1@gmail.com>
Fix function-not-used warnings detected by Clang 3.4

These functions have been turned to static (although inline), which
means they need to be used or marked as possibly unused.

qglobal.h:712:37: error: unused function 'qFuzzyCompare' [-Werror,-Wunused-function]

Change-Id: Ie2ee713d26c86e0574b579c1ea42b9404c3d2035
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
Fix unused function warnings in qtriangulator.cpp

qIntersectionPoint with ints wasn't used, qDot was only used in debug
mode. Found by Clang 3.4.

Change-Id: I4b5699f75eb88331df54bf5a289133914d80b299
Reviewed-by: Robin Burchell <robin+qt@viroteck.net>
Reviewed-by: Gunnar Sletta <gunnar.sletta@jollamobile.com>
Remove unused member m_eglApi

It's not used anywhere. Found by Clang 3.4:

qeglplatformcontext_p.h:80:13: error: private field 'm_eglApi' is not used [-Werror,-Wunused-private-field]

Change-Id: I37ce240a9d07ef570e0814de366dbb7cd13ad714
Reviewed-by: Robin Burchell <robin+qt@viroteck.net>
Fix QtWidget function-unused warnings found by Clang 3.4

qwidgetbackingstore.cpp:72:20: error: unused function 'qRectIntersects' [-Werror,-Wunused-function]

Change-Id: Ia3afe8f0547fa86804093281db89efabe68b34a1
Reviewed-by: Robin Burchell <robin+qt@viroteck.net>
Don't check if a file exists before opening it

If the file doesn't exist, open() will fail. But open() might fail
even if the file exists(), which would lead to bad follow-up code. In
any case, this saves one unnecessary stat(2).

Change-Id: Ic99507c9dc07a4387ee6a4fe9c24830fca54e095
Reviewed-by: Robin Burchell <robin+qt@viroteck.net>
Make qtbase compile with QT_NO_XMLSTREAMWRITER

Change-Id: I6d2447ba0875117e8a50d1aa3133bd5ea098d51a
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>