Merge #87: cmake: Bug fixes

63c1bb5 fixup! cmake: Add fuzzing options (Hennadii Stepanov)
d31abc2 fixup! ci: Test CMake edge cases (Hennadii Stepanov)

Pull request description:

  From #85 (comment):
  > **Known Bugs**
  >
  > Unfortunately, due to a silent conflict between #43 and #77, providing `-DFUZZ=ON` does not disable the `bitcoin-qt` target. It will be fixed shortly after pushing this branch.

  Fixed.

ACKs for top commit:
  vasild:
    ACK 63c1bb5

Tree-SHA512: b3cc2889d0239913de64c170880c97b37966a890d8c4e05f9090485a016b7f9cdf4880d770a234f323d3191b9adda8ed0343c29dfa49b5bb99b0b54481d4335e

CMakeLists.txt

@@ -84,6 +84,7 @@ if(FUZZ)
   set(BUILD_UTIL_CHAINSTATE OFF)
   set(BUILD_SHARED_LIBS OFF)
   set(BUILD_WALLET_TOOL OFF)
+  set(WITH_GUI OFF)
   set(WITH_NATPMP OFF)
   set(WITH_MINIUPNPC OFF)
   set(WITH_ZMQ OFF)