Add -Wimplicit-fallthrough warning flag, which warns on fallthrough between
cases in switch statements. Also add a [[clang::fallthrough]] attribute, which
can be used to suppress the warning in the case of intentional fallthrough.

Patch by Alexander Kornienko!

The handling of C++11 attribute namespaces in this patch is temporary, and will
be replaced with a cleaner mechanism in a subsequent patch.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@156086 91177308-0d34-0410-b5e6-96231b3b80d8
12 files changed