btrfs-progs: build: use -O2 by default

There's no obvious reason why there's -O1 instead -O2 which is commonly
used on distro builds. -O1 was enabled in c1690a3 ("Switch to -O1
for optimizations to enable FORTIFY_SOURCE") for the fortify checks.

Signed-off-by: David Sterba <dsterba@suse.com>

Author: kdave

configure.ac

@@ -24,7 +24,7 @@ BTRFS_UTIL_VERSION_MAJOR=`sed -rn 's/^\#define BTRFS_UTIL_VERSION_MAJOR ([0-9])+
 BTRFS_UTIL_VERSION_MINOR=`sed -rn 's/^\#define BTRFS_UTIL_VERSION_MINOR ([0-9])+$/\1/p' libbtrfsutil/btrfsutil.h`
 BTRFS_UTIL_VERSION_PATCH=`sed -rn 's/^\#define BTRFS_UTIL_VERSION_PATCH ([0-9])+$/\1/p' libbtrfsutil/btrfsutil.h`
 
-CFLAGS=${CFLAGS:-"-g -O1 -Wall -D_FORTIFY_SOURCE=2"}
+CFLAGS=${CFLAGS:-"-g -O2 -Wall -D_FORTIFY_SOURCE=2"}
 AC_SUBST([CFLAGS])
 
 AC_PREREQ([2.60])