Store result of try compile in cache variable?

[jdumas]

Hi,

Those try_compile are quite expensive to re-run each time CMake is called:

boost-cmake/libs/log.cmake

Line 65 in 70b12f6

try_compile(HAVE_PTHREAD_MUTEX_ROBUST

It would be better to store the result in a CACHE variable (using a prefix to avoid collisions), to speed up project reconfiguration.