Do not directly override libc symbols from the library.

Instead we export _override symbols and add the symbol
renaming directly into the QtWebEngineProcess source.

Change-Id: I209a7dcf42772bb993e966f253dd2d1c7013dceb
Reviewed-by: Andras Becsi <andras.becsi@digia.com>
Adjust gyp defines for eLinux.

- Add Raspberry PI chipset to list of defined platforms.
- Make sure to include sources for xdg support.
- Do not use pkg-config-wrapper, as our sysroot pkg-config
  already returns absolute paths.
- Use openssl for eLinux.
- Use fontconfig and freetype2 for eLinux.
- Use chacha_vec.c to avoid hard/soft float mismatch.

Change-Id: I8dd21c480922f32ac7111ea5582d82c249414caa
Reviewed-by: Pierre Rossi <pierre.rossi@gmail.com>