Merge #38

38: link.x: Add .sdata2 sections r=Disasm a=laanwj

Clang doesn't seem to generate these, but GCC (8.3.0 at least) does. I'm trying to link secp256k1, which is a C library, to my Rust code so the linker script needs to include these sections too.

Co-authored-by: Wladimir J. van der Laan <laanwj@gmail.com>