Fix uninitialized variables, and use -O so gcc starts checking for them

Gcc only sends warnings for uninitialized variables when you compile with -O,
and there were a couple of bugs sprinkled in the code.  The biggest was the
alloc_start variable for mkfs, which can cause strange things to happen.

(thanks to Gabor Micsko for helping to find this)

Makefile

@@ -1,6 +1,6 @@
 CC=gcc
 AM_CFLAGS = -Wall -fno-strict-aliasing -D_FILE_OFFSET_BITS=64 -D_FORTIFY_SOURCE=2
-CFLAGS = -g -Werror
+CFLAGS = -g -Werror -Os
 objects = ctree.o disk-io.o radix-tree.o extent-tree.o print-tree.o \
 	  root-tree.o dir-item.o hash.o file-item.o inode-item.o \
 	  inode-map.o crc32c.o rbtree.o extent-cache.o extent_io.o \

btrfs-vol.c

@@ -71,9 +71,9 @@ int main(int ac, char **av)
 	char *mnt = NULL;
 	int ret;
 	int option_index = 0;
-	int cmd;
+	int cmd = 0;
 	int fd;
-	int devfd;
+	int devfd = 0;
 	DIR *dirstream;
 	struct btrfs_ioctl_vol_args args;
 	u64 dev_block_count = 0;

mkfs.c

@@ -308,7 +308,7 @@ int main(int ac, char **av)
 	u64 block_count = 0;
 	u64 dev_block_count = 0;
 	u64 blocks[6];
-	u64 alloc_start;
+	u64 alloc_start = 0;
 	u64 metadata_profile = BTRFS_BLOCK_GROUP_RAID1 | BTRFS_BLOCK_GROUP_DUP;
 	u64 data_profile = BTRFS_BLOCK_GROUP_RAID0;
 	u32 leafsize = getpagesize();

utils.c

@@ -645,7 +645,7 @@ int btrfs_register_one_device(char *fname)
 
 int btrfs_scan_one_dir(char *dirname, int run_ioctl)
 {
-	DIR *dirp;
+	DIR *dirp = NULL;
 	struct dirent *dirent;
 	struct pending_dir *pending;
 	struct stat st;
@@ -734,7 +734,8 @@ again:
 	ret = 0;
 fail:
 	free(pending);
-	closedir(dirp);
+	if (dirp)
+		closedir(dirp);
 	return ret;
 }