WinRT: Basic global support

Various global changes, primarily preprocessor flow, to support the
WinRT platform.

Change-Id: I3fa9cf91d5fb24019362e88fcf205e31b4f810b5
Reviewed-by: Andrew Knight <andrew.knight@digia.com>
Fixed compilation of QSystemsemaphore for WinRT

As CreateSemaphore and WaitForSingleObject are
not supported on WinRT their supported alternatives
are used.

Change-Id: I1aa20076e286ed8ae28ba332bbed41ff8ce0feff
Reviewed-by: Andrew Knight <andrew.knight@digia.com>
Reviewed-by: Maurice Kalinowski <maurice.kalinowski@digia.com>
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
WinRT: Shared memory support

WinRT supports in-memory file mapping via CreateFileMappingFromApp. This
is unimplemented on Windows Phone.

Change-Id: Ic5692e501cd2fe9e1337829bdeb933fccc804abe
Done-with: Andrew Knight
Reviewed-by: Maurice Kalinowski <maurice.kalinowski@digia.com>
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
WinRT: Compile fix for qelapsedtimer_win.cpp

Change-Id: I1c9d6904eecd499ca8c2b744e8ac60696f40c20f
Reviewed-by: Andrew Knight <andrew.knight@digia.com>
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
QT_NO_PROCESS for WinRT

As Windows Runtime does not really support the use
of spawning processes QT_NO_PROCESS is defined for
winrt builds and the corresponding sources are
excluded from build.

Change-Id: I79263417c985b23678c55ac44a5591a9a69d3c13
Reviewed-by: Andrew Knight <andrew.knight@digia.com>
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>
WinRT: QLibrary & plugin support

Avoid unsupported Win32 API while providing alternative codepaths for
in-package library loading.

Change-Id: Iaad059d6c94d0347cbaa8d9b9240806afcb29561
Done-with: Andrew Knight
Done-with: Kamil Trzcinski
Reviewed-by: Andrew Knight <andrew.knight@digia.com>
Reviewed-by: Oliver Wolff <oliver.wolff@digia.com>
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
libpng: Add WinRT compatibility

A _WINRT_ macro is added for Windows Runtime and a few codepaths are
changed with it.

Change-Id: I99ca5636d03c39b0a05b7f75f13522d012fdec07
Done-with: Andrew Knight <andrew.knight@digia.com>
Reviewed-by: Oliver Wolff <oliver.wolff@digia.com>