ci: Do not override `-g -O1` set in `MSAN_FLAGS`

Additionally, setting the "Debug" build configuration ensures that
`linux_debug_CPPFLAGS` from depends are passed to the main build system.

ci/test/00_setup_env_native_fuzz_with_msan.sh

@@ -17,8 +17,12 @@ export PACKAGES="ninja-build"
 # BDB generates false-positives and will be removed in future
 export DEP_OPTS="DEBUG=1 NO_BDB=1 NO_QT=1 CC=clang CXX=clang++ CFLAGS='${MSAN_FLAGS}' CXXFLAGS='${MSAN_AND_LIBCXX_FLAGS}'"
 export GOAL="install"
+# Setting CMAKE_{C,CXX}_FLAGS_DEBUG flags to an empty string ensures that the flags set in MSAN_FLAGS remain unaltered.
 # _FORTIFY_SOURCE is not compatible with MSAN.
 export BITCOIN_CONFIG="\
+ -DCMAKE_BUILD_TYPE=Debug \
+ -DCMAKE_C_FLAGS_DEBUG='' \
+ -DCMAKE_CXX_FLAGS_DEBUG='' \
  -DBUILD_FOR_FUZZING=ON \
  -DSANITIZERS=fuzzer,memory \
  -DAPPEND_CPPFLAGS='-DBOOST_MULTI_INDEX_ENABLE_SAFE_MODE -U_FORTIFY_SOURCE' \

ci/test/00_setup_env_native_msan.sh

@@ -17,8 +17,15 @@ export PACKAGES="ninja-build"
 # BDB generates false-positives and will be removed in future
 export DEP_OPTS="DEBUG=1 NO_BDB=1 NO_QT=1 CC=clang CXX=clang++ CFLAGS='${MSAN_FLAGS}' CXXFLAGS='${MSAN_AND_LIBCXX_FLAGS}'"
 export GOAL="install"
+# Setting CMAKE_{C,CXX}_FLAGS_DEBUG flags to an empty string ensures that the flags set in MSAN_FLAGS remain unaltered.
 # _FORTIFY_SOURCE is not compatible with MSAN.
-export BITCOIN_CONFIG="-DSANITIZERS=memory -DAPPEND_CPPFLAGS='-U_FORTIFY_SOURCE'"
+export BITCOIN_CONFIG="\
+ -DCMAKE_BUILD_TYPE=Debug \
+ -DCMAKE_C_FLAGS_DEBUG='' \
+ -DCMAKE_CXX_FLAGS_DEBUG='' \
+ -DSANITIZERS=memory \
+ -DAPPEND_CPPFLAGS='-U_FORTIFY_SOURCE' \
+"
 export USE_MEMORY_SANITIZER="true"
 export RUN_FUNCTIONAL_TESTS="false"
 export CCACHE_MAXSIZE=250M