Fixes for the NAG Fortran compiler

[ACSimon33]

Description

There were several things the NAG Fortran compiler complained about in the current master branch:

• The new nrm2 tests use [S,D]XVALS which return -Inf, Inf, or NaN. This trips up nagfor's constant propagation. I disabled constant propagation for the BLAS test executables.
• Some FORMAT specifiers were longer than 72 characters
• Some intrinsic functions were missing
• Non-standard imag was used

Checklist

• [N/A] The documentation has been updated.
• [N/A] If the PR solves a specific issue, it is set to be closed on merge.