rules: update CFLAGS to match upstream

Author: merge

debian/rules

@@ -10,7 +10,7 @@ CROSS= --build $(DEB_BUILD_GNU_TYPE)
 endif
 
 export DEB_LDFLAGS_MAINT_APPEND = -Wl,--as-needed
-export DEB_CFLAGS_MAINT_APPEND = -O2 -Wall -W
+export DEB_CFLAGS_MAINT_APPEND = -O2 -Wall -W -fPIC
 export DEB_BUILD_MAINT_OPTIONS = hardening=+all
 
 #DH_VERBOSE = 1