[SCEV] Avoid repeated proveNoSignedWrapViaInduction calls.

 At the moment, proveNoSignedWrapViaInduction may be called for the
same AddRec a large number of times via getSignExtendExpr. This can have
a severe compile-time impact for very loop-heavy code.

If proveNoSignedWrapViaInduction failed to prove NSW the first time,
it is unlikely to succeed on subsequent tries and the cost doesn't seem
to be justified.

This is the signed version of 8daa3382 / D130648.

This can drastically improve compile-time in some excessive cases and
also has a slightly positive compile-time impact on CTMark:

NewPM-O3: -0.06%
NewPM-ReleaseThinLTO: -0.04%
NewPM-ReleaseLTO-g: -0.04%

https://llvm-compile-time-tracker.com/compare.php?from=8daa338297d533db4d1ae8d3770613eb25c29688&to=aed126a196e7a5a9803543d9b4d6bdb233d0009c&stat=instructions

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D130694