cmdutils: add -cpuflags.

This allows globally forcing specific cpuflags (or lack thereof)
Useful for debugging and benchmarking

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

cmdutils_common_opts.h

@@ -16,3 +16,4 @@
     { "debug", HAS_ARG, {(void*)opt_codec_debug}, "set debug flags", "flags" },
     { "report", 0, {(void*)opt_report}, "generate a report" },
     { "max_alloc", HAS_ARG, {(void*)opt_max_alloc}, "set maximum size of a single allocated block", "bytes" },
+    { "cpuflags", HAS_ARG, {(void*)opt_cpuflags}, "force specific cpu flags", "flags" },