build-sys: don't set CFLAGS and LDFLAGS

These variables are supposed to be set by user. What we can do in
configure is to set another variable and AC_SUBST() it. Then in
Makefile.am we assign it to AM_{CFLAGS,LDFLAGS}. This way user can
always override their values, in configure or make phase.

Reference: http://www.gnu.org/software/automake/manual/html_node/Flag-Variables-Ordering.html
3 files changed