iperf-2.0.5-r2: x86_64-cros-linux-gnu-clang++ -DHAVE_CONFIG_H -I. -I. -I..  -I../include -I../include  -Wall -O2 -pipe -O2 -pipe -O2 -pipe -march=core2 -fno-exceptions -fno-unwind-tables   -fno-asynchronous-unwind-tables  -clang-syntax  -c -o delay.o delay.cpp

iperf-2.0.5-r2: In file included from delay.cpp:53:
iperf-2.0.5-r2: In file included from ../include/Timestamp.hpp:63:
iperf-2.0.5-r2: In file included from ../include/headers.h:85:
iperf-2.0.5-r2: In file included from /usr/bin/../include/c++/v1/math.h:312:
iperf-2.0.5-r2: /usr/bin/../include/c++/v1/type_traits:694:29: error: redefinition of '__libcpp_is_integral<int>'
iperf-2.0.5-r2: template <>          struct __libcpp_is_integral<int>                : public true_type {};
iperf-2.0.5-r2:                             ^~~~~~~~~~~~~~~~~~~~~~~~~
iperf-2.0.5-r2: /usr/bin/../include/c++/v1/type_traits:683:29: note: previous definition is here
iperf-2.0.5-r2: template <>          struct __libcpp_is_integral<bool>               : public true_type {};
iperf-2.0.5-r2:                             ^
iperf-2.0.5-r2: /usr/bin/../include/c++/v1/type_traits:1894:20: error: redefinition of '__make_signed<int, 1>'
iperf-2.0.5-r2: template <> struct __make_signed<  signed int,       true> {typedef int       type;};
iperf-2.0.5-r2:                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
iperf-2.0.5-r2: /usr/bin/../include/c++/v1/type_traits:1891:20: note: previous definition is here
iperf-2.0.5-r2: template <> struct __make_signed<bool,               true> {};

Interestingly, net-misc/iperf-3.1.3 builds without any issues.