Support (or ignore) `gcc`-specific switches while analyzing in `clang` toolchain

[ladisgin]

Then compile gcc project into bitcode by clang use flag --with-gcc-toolchain.
And add white or black list for flags
in KleeGenerator.cpp:128

[ladisgin]

some flags:

-fbranch-target-load-optimize
-fcx-fortran-rules
-fipa-cp-clone
-fipa-cp-cloneclang-10
-fira-loop-pressure
-fno-forward-propagate
-fno-if-conversion
-fno-sched-interblock
-fno-sched-spec-insn-heuristic
-fno-tree-dominator-opts
-fno-tree-sink
-fno-tree-sinkclang-10
-fpredictive-commoning
-freschedule-modulo-scheduled-loops
-fsched2-use-superblocks
-fsel-sched-reschedule-pipelined
-ftree-loop-distribute-patterns