PETSc: build optimized library unless DEBUG=yes

[Roland Haas]

When Cactus builds PETSc from the sources included in ExternalLibraries/PETSc it currently uses PETSc’s default build options which create a debug build, which is not giving good performance.

Pull request https://github.com/EinsteinToolkit/ExternalLibraries-PETSc/pull/2 makes Cactus build an optimized version unless DEBUG=yes is set.

[Roland Haas]

Please review.

[Roland Haas]

Unless objected I will apply this after 2021-02-18

[Roland Haas]

Applied as git hash 4bed79e "PETSc: build optimized library unless DEBUG=yes" of ExternalLibraries-PETSc