GRIT should use unix file paths as dictionary keys on Windows

GRIT uses filename strings as keys in its dictionary so generated
filenames must be exactly the same strings as they are defined in
.grd files. GRIT expects forward slashes as path separator and
also .grd files are containing forward slashes.
Similar conversion used in the else section of the outer
if statement in the same function.

Change-Id: I81bbf2e15e7aaefb52176405990d49457fce1589
Reviewed-by: Andras Becsi <andras.becsi@digia.com>
Fix missing include in DxDiagNode

DxDiagNode needs build_config.h when using OS_WIN guard.

Change-Id: I15e2b115bf41cd648dafecb362d81f0b8722d485
Reviewed-by: Andras Becsi <andras.becsi@digia.com>
Extend search path in libvpx to enable build with QtWebEngine

Paths are paritally hardcoded for Windows in libvpx.

Change-Id: Ic1c537bcc8b988c9803326709e38f44cb0943ee3
Reviewed-by: Andras Becsi <andras.becsi@digia.com>