Fix Qt rcc's path in Qt5WebEngineCore.ninja on Windows.

On Windows backslash in QMAKE_RCC causes wrongly generated Qt5WebEngineCore.ninja file.

For example QMAKE_RCC's value generated to lib/lib.gyp as 'c:\Qt-5.2.0\bin\rcc.exe'.
This turns to 'c:/Qt-5.2.0[BS]in[CR]cc.exe' in Qt5WebEngineCore.ninja after running qyp.
That means \b is parsed as backspace and \r is pharsed as carriage return character.
Current Windows versions can handle forward slashes in paths so backslashes can be replaced to forward slashes when needed.

Change-Id: I814dc63df92b78ed5cae028e0b8c36dbf3eb1e49
Reviewed-by: Andras Becsi <andras.becsi@digia.com>
Reviewed-by: Pierre Rossi <pierre.rossi@gmail.com>
Fix path for webkit_strings gypi dependency on Windows.

Windows specific dependency points to the wrong path.

Change-Id: Ib94f15e8872666c716ad6093b1f0ca957a050db7
Reviewed-by: Andras Becsi <andras.becsi@digia.com>