[Bug fortran/77897] Compile error with KNL & -O3 for GTC code

[longb at cray dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77897

--- Comment #1 from Bill Long <longb at cray dot com> ---
Compiling these files appears to have a problem when the target is set to Intel
KNL.  The compiler appears to be generating incorrect register and instruction
names, leading to assembler messages.  See with gfortran 6.2.

Compiles OK with any of these changes:

1) Change target to Sandybridge
2) Remove the -O3 option
3) Use a different vendor compiler (Cray)