This adds powerpc64-specific test cases in 'test_usdt_args'
and also updates the folly tracing headers to be able to
produce compatible USDT markers for 'test_usdt'. The folly
tracing ELF header now provides macros for all supported
architectures instead of just x86.
Signed-off-by: Sandipan Das <sandipan@linux.vnet.ibm.com>