[libFuzzer] Disable merge-sigusr.test on linux.
Make buildbot green while I rethink the test.
# Check that libFuzzer honors SIGUSR1/SIGUSR2
# FIXME: Disabled on Windows for now because of reliance on posix only features
# (eg: export, "&", pkill).
-UNSUPPORTED: darwin, windows
+# TODO(morehouse): rethink test and reenable for linux.
+UNSUPPORTED: darwin, windows, linux
RUN: rm -rf %t
RUN: mkdir -p %t
RUN: %cpp_compiler %S/SleepOneSecondTest.cpp -o %t/LFSIGUSR
