Makefile: Modify default CFLAGS

This removes the "-g -O0" default (to leave them up to the user
CFLAGS), and adds a switch to ignore "unused result" warnings.
The latter is relevant when trying to compile nand-part.c with
optimizations enabled.
Signed-off-by: Bernhard Nortmann <bernhard.nortmann@web.de>

.travis.yml

@@ -5,7 +5,7 @@ language: c
 
 # treat all warnings as errors, fake cross-toolchain (build everything on host)
 env:
-  - CFLAGS=-Werror CROSS_COMPILE=""
+  - CFLAGS="-g -O2 -Werror" CROSS_COMPILE=""
 
 os:
   - linux

Makefile

@@ -17,7 +17,8 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 CC ?= gcc
-DEFAULT_CFLAGS := -g -O0 -Wall -Wextra -std=c99
+DEFAULT_CFLAGS := -std=c99
+DEFAULT_CFLAGS += -Wall -Wextra -Wno-unused-result
 
 DEFAULT_CFLAGS += -D_POSIX_C_SOURCE=200112L
 # Define _BSD_SOURCE, necessary to expose all endian conversions properly.