FindLAPACK: Distinguish check result variable name from FindBLAS
Since commit 192a9182f8 (FindLAPACK: MKL clean up and fix for windows,
2013-10-08, v3.0.0-rc1~538^2), FindLAPACK accidentally used FindBLAS's
`BLAS_` prefix for some of its check results.
Since commit 5b8f69ebe9 (FindBLAS: Detect implicitly linked BLAS
library, 2018-08-28, v3.13.0-rc1~150^2~2), FindBLAS stores a check
result in a plain `BLAS_WORKS` variable. The typo in FindLAPACK happens
to cause a collision with that name.
The typo was already fixed in post-3.13 development as part of other
work in commit 8b63265ea5 (FindLAPACK: Unify internal variables related
to MKL, 2018-11-18). Fix the typo in the 3.13 version of FindLAPACK to
avoid the collision. Otherwise it could cause FindLAPACK to incorrectly
determine that a certain library combination does not work (or
incrrectly that it works).
Fixes: #18860
Brad King