Move dependencies in 'external' directory and pdate git submodules

external/Catch2/fuzzing/CMakeLists.txt

@@ -0,0 +1,20 @@
+# License: Boost 1.0
+# By Paul Dreik 2020
+
+# add a library that brings in the main() function from libfuzzer
+# and has all the dependencies, so the individual fuzzers can be
+# added one line each.
+add_library(fuzzhelper NullOStream.h NullOStream.cpp)
+target_link_libraries(fuzzhelper PUBLIC Catch2::Catch2)
+
+# use C++17 so we can get string_view
+target_compile_features(fuzzhelper PUBLIC cxx_std_17)
+
+# This should be possible to set from the outside to be oss-fuzz compatible,
+# fix later. For now, target libFuzzer only.
+target_link_options(fuzzhelper PUBLIC "-fsanitize=fuzzer")
+
+foreach(fuzzer TestSpecParser XmlWriter textflow)
+add_executable(fuzz_${fuzzer} fuzz_${fuzzer}.cpp)
+target_link_libraries(fuzz_${fuzzer} PRIVATE fuzzhelper)
+endforeach()