Rename warn_drv_overriding_flag_option (-Woverriding-t-option) to...

Rename warn_drv_overriding_flag_option (-Woverriding-t-option) to warn_drv_overriding_flag_option (-Woverriding-option)

warn_drv_overriding_flag_option was added for clang-cl `/T*` options (D1290) and its group name was planned to be renamed to overriding-option.
The name -Woverriding-t-option does not make sense for other uses,
mostly related to -ffp-model= related diagnostics.

Reviewed By: hans, skan, dexonsmith

Differential Revision: https://reviews.llvm.org/D158137