Fix CFLAGS once and for all

Makefile

@@ -1,4 +1,4 @@
-CFLAGS = -O3 std=c99 -Wall -D_POSIX_C_SOURCE=200809L
+export CFLAGS += -O3 -std=c99 -Wall -D_POSIX_C_SOURCE=200809L
 
 all:
 	@${MAKE} -C tiff

c.mk

@@ -37,8 +37,7 @@ else
 	PKG_LDFLAGS =
 endif
 
-CFLAGS ?= -Wall -Werror -O2
-CFLAGS += $(PKG_CFLAGS) -std=c99
+CFLAGS += $(PKG_CFLAGS)
 LDFLAGS += $(PKG_LDFLAGS)
 
 # GNU-compliant install directories