The test case optnone-simple-functions.cpp is expected to be compiled
unoptimized even under -O2 because of attribute optnone. But this attribute is
missed for main function, and caused the fail in
https://lab.llvm.org/buildbot/#/builders/217/builds/14046 when it triggered
optimizations. This patch fixes that by adding attribute optnone to main
function.
Differential Revision: https://reviews.llvm.org/D136778