Patch libblst to overcome duplicate symbol definition problem

[neilmayhew]

Before:

$ nm -og libblst.a | grep __blst_platform_cap
libblst.a:assembly.o:0000000000000004 C __blst_platform_cap
libblst.a:server.o:0000000000000000 B __blst_platform_cap

After:

$ nm -og libblst.a | grep __blst_platform_cap
libblst.a:assembly.o:0000000000000004 C __blst_platform_cap
libblst.a:server.o:0000000000000004 C __blst_platform_cap

I tested this in cardano-ledger with:

$ nix flake update iohkNix --override-input iohkNix github:input-output-hk/iohk-nix/81fcdbc93c5514a8f133771b12b94d63f5d859af
$ nix develop -c cabal test all