Issue cflags

First commit allow to honours system CFLAGS, which is mandatory during RPM build, by Guidelines.

FYI, default Fedora CFLAGS are -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector --param=ssp-buffer-size=4 -grecord-gcc-switches  -m64 -mtune=generic

Second commit reduce optional flags which raise a lot of warnings during build (especially -Winline)