PR15755: don't drop parameter packs when dropping parameters with default
arguments in the formation of a candidate set of inheriting constructors.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@179708 91177308-0d34-0410-b5e6-96231b3b80d8
Fix off-by-one error in #pragma clang system_header.

The system_header pragma (from GCC) is implemented using line notes in the
source manager. However, a line note's line number specifies the number
not for the current line, but for the next line. This was making all
line numbers appear off by one after the pragma.

Reported by Andy Gibbs, uncovered during r179677.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@179709 91177308-0d34-0410-b5e6-96231b3b80d8