warnings about usage of C++ style comments

[tfarina]

cc unit_test.c -o unit_test -lpthread -W -Wall -pedantic -O0 -g -I.. -lssl
unit_test.c:1:1: warning: C++ style comments are not allowed in ISO C90 [enabled by default]
unit_test.c:1:1: warning: (this will be reported only once per input file) [enabled by default]
In file included from unit_test.c:13:0:
../net_skeleton.c:1:1: warning: C++ style comments are not allowed in ISO C90 [enabled by default]
../net_skeleton.c:1:1: warning: (this will be reported only once per input file) [enabled by default]
In file included from ../net_skeleton.c:17:0,
from unit_test.c:13:
../net_skeleton.h:1:1: warning: C++ style comments are not allowed in ISO C90 [enabled by default]
../net_skeleton.h:1:1: warning: (this will be reported only once per input file) [enabled by default]
clang nc.c ../net_skeleton.c -DNS_ENABLE_SSL -lssl -o nc -lpthread -W -Wall -pedantic -O0 -g -I..

[tfarina]

thanks!