update compiler warnings in Makefile
update compiler warnings in Makefile

* drop duplicate use of -Wextra, namely -W
* drop -Wno-long-long, long long is used
* drop -Wno-missing-field-initializers
* add -Wshadow and -Wold-style-definition

allinurl/goaccess,allinurl/goaccess,allinurl/goaccess,allinurl/goaccess