build: CPPFLAGS usage in OSS-Fuzz

[hebasto]

In OSS-Fuzz, dependencies are built with DEBUG=1, which implies usage of the additional preprocessor definitions:

$ make -C depends print-host_debug_CPPFLAGS HOST=x86_64-pc-linux-gnu DEBUG=1
...
host_debug_CPPFLAGS=-D_GLIBCXX_DEBUG -D_GLIBCXX_DEBUG_PEDANTIC -D_LIBCPP_ENABLE_DEBUG_MODE=1

However, explicit setting CPPFLAGS breaks this assumption:

$ make -C depends print-host_debug_CPPFLAGS HOST=x86_64-pc-linux-gnu DEBUG=1 CPPFLAGS="-DBOOST_MULTI_INDEX_ENABLE_SAFE_MODE"
...
host_debug_CPPFLAGS=-DBOOST_MULTI_INDEX_ENABLE_SAFE_MODE

Is this expected/desired behaviour?

[maflcko]

Reference: https://github.com/google/oss-fuzz/blob/c801e7aab5822e0c305fdb88dbe21b834d45afea/projects/bitcoin-core/build.sh#L38

[maflcko]

Same in ci/test/00_setup_env_native_fuzz_with_msan.sh?

[fanquake]

Should be closed after google/oss-fuzz#11725.