run cheats tests with both resolc and evm enabled

[alexggh]

Make the cheats tests run with both resolc and evm compilers.

Some of the tests have been disabled from compiling because it was failing to compile because of:

Error 1: solidity version not supported by resolc.

Encountered invalid solc version in default/fork/DssExecLib.sol: No solc version exists that matches the version requirement: >=0.6.12, <0.7.0\

Error 2: EXTCODECOPY instruction not supported

compiling error: The contract `default/cheats/AttachDelegation.t.sol:AttachDelegationTest` LLVM IR generator definition pass error: 256:25 The `EXTCODECOPY` instruction is not supportedThe contract `default/cheats/AttachDelegation.t.sol:AttachDelegationTest` LLVM IR generator definition pass error: 256:25 The `EXTCODECOPY` instruction is not supported")

Note the tests compile with resolc are currently failing, should start passing as more cheat code support is added.

Fixes: #300 .