libressl: fix musl build with older kernel headers

libressl: fix musl build with older kernel headers

musl provides its own SYS_getrandom definition, but not GRND_NONBLOCK.
This breaks the build with kernel headers older than v3.17. Add a patch
adding a local definition of GRND_NONBLOCK to fix the build.

The following defconfig reproduces the build failure:

BR2_x86_pentium_mmx=y
BR2_TOOLCHAIN_BUILDROOT_MUSL=y
BR2_KERNEL_HEADERS_3_12=y
BR2_PACKAGE_LIBRESSL=y

The getentropy_linux.c file is in upstream tarball, but not in its git
repository. It originates from OpenBSD. For this reason the patch is
against the tarball, but not git formatted.

Cc: Adam Duskett <aduskett@gmail.com>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
[Arnout: change filename to correspond to how git creates it]
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>