Fix use of an uninitialized SourceLocation because DeclarationNameLoc failed...

Fix use of an uninitialized SourceLocation because DeclarationNameLoc failed to completely zero-initialize itself.
Now we explicitly memset all of its values.

This bug was uncovered by the 'Index/recursive-cxx-member-calls.cpp', which exhibited an assertion
on an i386 darwin build of clang.  Adding this test case back since the assertion is now resolved.

llvm-svn: 118881