eal: fix C++ compilation after headers rework
eal: fix C++ compilation after headers rework

Following the big headers rework, all C++ stuff has moved to arch-specific
headers. The generic headers should not contain this so that this is done only
once.
There was a remaining #ifdef __cplusplus in "eal: split CPU cycle operation to
architecture specific" (fa4001c30ee9).

Reported-by: Keunhong Lee <7547ac7688dd73de7f18e13d46479026fbbecb1e@gmail.com>
Signed-off-by: David Marchand <f28529695cfa9e3e1eb84e7072aa626af4abb18e@6wind.com>
Acked-by: Thomas Monjalon <ee2fa8b2681c737f775687e475dcbf2028a412f1@6wind.com>

tsphillips/dpdk-fork,tsphillips/dpdk-fork,tsphillips/dpdk-fork,mixja/dpdk,john-mcnamara-intel/dpdk,venkynv/dpdk-mirror,msune/dpdk,mixja/dpdk,msune/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,venkynv/dpdk-mirror,msune/dpdk,venkynv/dpdk-mirror,venkynv/dpdk-mirror,john-mcnamara-intel/dpdk,mixja/dpdk,msune/dpdk,tsphillips/dpdk-fork,mixja/dpdk