Make sure that ClangExpressionDeclMap doesn't

live beyont parsing.  This is important because
all the ClangASTImporter::Minions for a parser's
ASTContext are cleared when ClangExpressionDeclMap
is deleted.

This resolves many hard-to-reproduce crashes,
especially ones involving breakpoint conditions.

<rdar://problem/14775391>

llvm-svn: 189080