Excesive test compile resources.

[grafikrobot]

While working on modular B2 Boost changes I've been having to run all the library test (and examples, etc) builds. Building the Math tests fully is essentially impossible on reasonable hardware. Multiple times running the tests causes my system, when using parallel compiling, to run out of RAM and use all CPU time available. There are some single tests that cause GCC to use up anywhere from 33% to 99% of RAM (yes just one cc1plus process). This has caused such runs to halt, die, and kill the whole parent process chain.

Please fix the tests so as to reduce the burden on everyone who runs testing (such as the expensive cloud CI providers).

[mborland]

Largest offending test suite should be mitigated by #965