[sanitizer-coverage/libFuzzer] make the guards for trace-pc 32-bit; create one array of guards per function, instead of one guard per BB. reorganize the code so that trace-pc-guard does not create unneeded globals

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@282735 91177308-0d34-0410-b5e6-96231b3b80d8