[clang] deduplicate target-features for modules (#187614)
Previously, double passing a target feature would make the module
incompatible with a compilation unit that only passes it once.
The motivating problem is, when we pass -target-features +tagged-globals
as well as -fsanitize=hwaddress, which adds a second copy, the module
is incompatible with one built with only one `-target-features
+tagged-globals`.
