[analyzer] Add support for testing the presence of weak functions.

When casting the address of a FunctionTextRegion to bool, or when adding
constraints to such an address, use a stand-in symbol to represent the
presence or absence of the function if the function is weakly linked.
This is groundwork for possible simple availability testing checks, and
can already catch mistakes involving inverted null checks for
weakly-linked functions.

Currently, the implementation reuses the "extent" symbols, originally created
for tracking the size of a malloc region. Since FunctionTextRegions cannot
be dereferenced, the extent symbol will never be used for anything else.
Still, this probably deserves a refactoring in the future.

This patch does not attempt to support testing the presence of weak
/variables/ (global variables), which would likely require much more of
a change and a generalization of "region structure metadata", like the
current "extents", vs. "region contents metadata", like CStringChecker's
"string length".

Patch by Richard <tarka.t.otter@googlemail.com>!

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@189492 91177308-0d34-0410-b5e6-96231b3b80d8
PR16995: Failing to associate static members with their enclosing class

In the transition from declaration (with some members) to definition, we
were overwriting the list of members with the empty list when attaching
template parameters.

The fix is in llvm::DICompositeType::addMember (along with asserts that
cause this bug to be covered by existing Clang test cases), including
adding some asserts to catch this sort of issue which found issues fixed
in this commit.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@189494 91177308-0d34-0410-b5e6-96231b3b80d8
clang-cl: Pass -debug to the linker when using -fsanitize=address

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@189496 91177308-0d34-0410-b5e6-96231b3b80d8