Added getTrueExpr() and getFalseExpr() to ConditionalOperator. These methods

provide handy accessors to the subexpressions of ConditionalOperator that
automatically take into account the GCC extension where the "LHS" expression is
omitted: e.g x ?: y;. When the LHS expression is available, getTrueExpr() is the
same as getLHS(); when LHS is NULL, getTrueExpr() returns the condition expression.

llvm-svn: 44536