d902dd011c
This patch basically implements [1] in ExecuteCompilerInvocation.cpp. It
also:
* replaces `CreateFrontendBaseAction` with `CreateFrontendAction`
(only one method is needed ATM, this change removes the extra
indirection)
* removes `InvalidAction` from the `ActionKind` enum (I don't think it
adds much and keeping it would mean adding a new void case in
`CreateFrontendAction`)
* sets the default frontend action in FrontendOptions.h to
`ParseSyntaxOnly` (note that this is still overridden independently
in `ParseFrontendArg` in CompilerInvocation.cpp)
No new functionality is added, hence no tests.
[1] https://llvm.org/docs/CodingStandards.html#don-t-use-default-labels-in-fully-covered-switches-over-enumerations
Differential Revision: https://reviews.llvm.org/D124245