[Users] Checking for strdup

With intel-13.2.146 compiler, I've observed that the configure check for strdup (lib/make/configure.in line 494, using CCTK_CHECK_HAS_PROTOTYPE) can fail despite strdup being defined in string.h.

The test for this seems to rely on compilation of "int strdup()" failing if this prototype exists, but on a machine I'm using currently, the intel compiler only generates a *warning*, not an *error*, and considers compilation to have "succeeded." Since compilation "succeeded", the test fails, even though strdup's prototype is available.

This can be worked around by adding -diag-error 147 (the id code for this diagnostic) to CFLAGS. Is this what end-users should be expected to do?

-Michael Clark