sdl: disable rpath via configure option

sdl: disable rpath via configure option

The -rpath option was being stripped from sdl-config via a post install
staging hook, but the same wasn't being done for sdl.pc. Because of
this, packages that detect SDL via pkg-config ended up passing
'-Wl,-rpath,/usr/lib' to the linker, which caused build failures under
certain circumstances since libraries were being looked for in the wrong
directory.

Fix by passing the --disable-rpath option to the SDL configure script,
which takes care of disabling -rpath everywhere. This also allows the
SDL_FIXUP_SDL_CONFIG hack to be completely removed.

Fixes:

  http://autobuild.buildroot.net/results/624/62499217eeaf3228b46652e3f65776d7ece8fce6/
  http://autobuild.buildroot.net/results/cc1/cc1f78f6c43e3a7bf3ed80d759d9c4d7363d0e48/

Signed-off-by: Rodrigo Rebello <rprebello@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>