The attached patch undefines USTRICT_ANSI on stampede, similar to other machines. One effect of this is that M_PI is defined when math.h is included. By default, the lib otherwise follows the strict standard that math.h is not to pollute the namespace and doesn't define M_PI because it is not in the ANSI standard (but e.g. in POSIX). The ET depends on M_PI being defined in several thorns and a discussion on this topic took place on the mailing list some time ago. The consensus there was to try to make sure with compiler flags that POSIX is available, and with that M_PI.
I committed this change to /trunk of simfactory already (in r2008), but want to have a positive review for a backport to Ørsted.