Prevent this by modifying CFLAGS and CXXFLAGS.

Upmerge from 5.0, modified according to the different spec file structure.

support-files/mysql.spec.sh:
  Bug #40546  Debug server in RPM is built with compiler optimization
  
  Modify CFLAGS and CXXFLAGS for the duration of the debug server build
  (implemented by doing it in a subshell)
  so that they do not contain any optimization flag.
  Play it safe and prepare for both gcc and icc.