remove explicit gcc dependencies
fix clang compile error (asm related) (see https://bitbucket.org/cgzones/ossec-hids/commits/1aa1d8b786d0ab730458626754b4666e4b7eb19d)
fix clang -Wall warnings (amend)
build endian binary with general cc compiler (instead require gcc)
update make targets make setclang and unsetclang
travis: enable clang and geoip
remove explicit CC assignment
using cc as default compiler and preserve setclang setting
fix make unsetclang
only assign CC if empty (CC may be exported globally, e.g. by travis: export CC=clang)