In jdk/make/modules/java.desktop/lib/ClientLibraries.gmk, in the section for building libfontmanager, there is a section for defining HARFBUZZ_DISABLED_WARNINGS_CXX_gcc.

https://github.com/openjdk/jdk/blame/32c975098521e830ce706b67e7232a007c0846c7/make/modules/java.desktop/lib/ClientLibraries.gmk#L313-L320

There is a preceding comment mentioning several warnings being suppressed for older gcc versions and not needing suppression for indicated later vresions. The current minimum supported gcc version is 10 (JDK-8325881), so some of those suppressions should no longer be needed. Specifically

- noexcept-type not needed for gcc 8+
- expansion-to-defined not needed for gcc 10+
- maybe-uninitialized not needed for gcc 9+