Disable fmaxmin_test when compiling it with clang 3.8.0

The testcase always fails today due to how C11 7.6.1/2 is interpreted
with clang 3.8.0 when combined with "#pragma STDC FENV_ACCESS ON".

This testcase passes with clang <3.8.0 and gcc, so continue testing it
with those compiler combinations

More intelligent discussion on the issue is in the PR

MFC after: never
PR: 208703
Sponsored by: EMC / Isilon Storage Division