build: replace add_compile_definitions

[compnerd]

Replace add_compile_definitions with add_compile_options since the
former was introduced in 3.12.

[compnerd]

@jgm sorry about the compatibility issue, this should fix that.

[jgm]

Thank you!

[jgm]

@compnerd I've been seeing this build failure on our fuzzing setup; I don't know if it has to do with your changes, but they're the most recent changes to the build infrastructure. Also paging @nwellnhof

https://oss-fuzz-build-logs.storage.googleapis.com/log-0d4dbbcd-58ba-4341-9359-708e4381d3df.txt

The error is

Step #4: clang-10: error: no such file or directory: 'build/src/libcmark.a'

Is it possible that one of the changes you made broke this?
Here is the bug report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=19805#c2

[compnerd]

I think its probably related ...

Step #4: + clang++ -O1 -fno-omit-frame-pointer -gline-tables-only -DFUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION -fsanitize=address -fsanitize-address-use-after-scope -fsanitize=fuzzer-no-link -stdlib=libc++ -fsanitize=fuzzer cmark_fuzzer.o build/src/libcmark.a -o /workspace/out/address/cmark_fuzzer

Note that it is trying to link against libcmark.a, yet the build will be producing libcmark_static.a as per https://github.com/commonmark/cmark/blob/master/src/CMakeLists.txt#L6 (which existed prior to my changes).

I don't immediately see where this command is coming from:

Step #4: + clang++ -O1 -fno-omit-frame-pointer -gline-tables-only -DFUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION -fsanitize=address -fsanitize-address-use-after-scope -fsanitize=fuzzer-no-link -stdlib=libc++ -fsanitize=fuzzer cmark_fuzzer.o build/src/libcmark.a -o /workspace/out/address/cmark_fuzzer

[nwellnhof]

No, it was libcmark.a before. This should fix it: #324