Avoid undefined behavior in shift operators during constant folding of DIExpressions. (#116466) Bit shift operations with a shift operand greater than or equal to the bit width of the (promoted) value type result in undefined behavior according to C++ [expr.shift]p1. This change adds checking for this situation and avoids attempts to constant fold DIExpressions that would otherwise provoke such behavior. An existing test that presumably intended to exercise shifts at the UB boundary has been updated; it now checks for shifts of 64 bits instead of 65. This issue was reported by a static analysis tool; no actual cases of shift operations that would result in undefined behavior in practice have been identified.
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