configure: fixup build so that it's more resilient

Allow people to clear/set EXTFLAGS/OPTFLAGS at will.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/Makefile b/Makefile
index ea96a89..27e82c6 100644
--- a/Makefile
+++ b/Makefile
@@ -1,11 +1,3 @@
-DEBUGFLAGS = -D_FORTIFY_SOURCE=2 -DFIO_INC_DEBUG
-CPPFLAGS= -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 $(DEBUGFLAGS)
-OPTFLAGS= -O3 -g -ffast-math $(EXTFLAGS)
-CFLAGS	= -std=gnu99 -Wwrite-strings -Wall $(OPTFLAGS)
-LIBS	= -lm $(EXTLIBS)
-PROGS	= fio
-SCRIPTS = fio_generate_plots
-
 ifneq ($(wildcard config-host.mak),)
 all:
 include config-host.mak
@@ -20,6 +12,14 @@
 include config-host.mak
 endif
 
+DEBUGFLAGS = -D_FORTIFY_SOURCE=2 -DFIO_INC_DEBUG
+CPPFLAGS= -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 $(DEBUGFLAGS)
+OPTFLAGS= -O3 -g -ffast-math
+CFLAGS	= -std=gnu99 -Wwrite-strings -Wall $(OPTFLAGS) $(EXTFLAGS) $(BUILD_CFLAGS)
+LIBS	+= -lm $(EXTLIBS)
+PROGS	= fio
+SCRIPTS = fio_generate_plots
+
 SOURCE := gettime.c fio.c ioengines.c init.c stat.c log.c time.c filesetup.c \
 		eta.c verify.c memory.c io_u.c parse.c mutex.c options.c \
 		rbtree.c smalloc.c filehash.c profile.c debug.c lib/rand.c \
diff --git a/configure b/configure
index 836d7ad..a3c51fb 100755
--- a/configure
+++ b/configure
@@ -38,8 +38,8 @@
 }
 
 # Default CFLAGS
-CFLAGS="-D_GNU_SOURCE"
-EXTFLAGS="-include config-host.h"
+CFLAGS="-D_GNU_SOURCE -include config-host.h"
+BUILD_CFLAGS=""
 
 # Print a helpful header at the top of config.log
 echo "# FIO configure log $(date)" >> config.log
@@ -230,7 +230,7 @@
   output_sym "CONFIG_SCHED_IDLE"
   output_sym "CONFIG_TCP_NODELAY"
   echo "CC=$CC" >> $config_host_mak
-  echo "EXTFLAGS=$CFLAGS -include config-host.h -D_GNU_SOURCE" >> $config_host_mak
+  echo "BUILD_CFLAGS=$CFLAGS -include config-host.h -D_GNU_SOURCE" >> $config_host_mak
   exit 0
   ;;
 esac
@@ -1088,4 +1088,4 @@
 
 echo "LIBS+=$LIBS" >> $config_host_mak
 echo "CC=$cc" >> $config_host_mak
-echo "EXTFLAGS=$EXTFLAGS $CFLAGS" >> $config_host_mak
+echo "BUILD_CFLAGS=$BUILD_CFLAGS $CFLAGS" >> $config_host_mak