Fix build error(ISO C90 specs violation) in lxc.c

Fix build error(ISO C90 specs violation) in lxc.c

This patch fixes following build errors.

running build_ext
building '_lxc' extension
creating build/temp.linux-x86_64-3.4
gcc -pthread -Wno-unused-result -Werror=declaration-after-statement -DDYNAMIC_ANNOTATIONS_ENABLED=1 -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes -march=x86-64 -mtune=generic -O2 -pipe -fstack-protector-strong --param=ssp-buffer-size=4 -fPIC -I../../src -I../../src -I/usr/include/python3.4m -c lxc.c -o ./build/temp.linux-x86_64-3.4/lxc.o
lxc.c: In function ‘convert_tuple_to_char_pointer_array’:
lxc.c:49:5: error: ISO C90 forbids mixed declarations and code [-Werror=declaration-after-statement]
     char **result = (char**) calloc(argc + 1, sizeof(char*));
     ^
lxc.c:60:9: error: ISO C90 forbids mixed declarations and code [-Werror=declaration-after-statement]
         char *str = NULL;
         ^
lxc.c: In function ‘Container_get_cgroup_item’:
lxc.c:822:5: error: ISO C90 forbids mixed declarations and code [-Werror=declaration-after-statement]
     char* value = (char*) malloc(sizeof(char)*len + 1);
     ^
lxc.c: In function ‘Container_get_config_item’:
lxc.c:861:5: error: ISO C90 forbids mixed declarations and code [-Werror=declaration-after-statement]
     char* value = (char*) malloc(sizeof(char)*len + 1);
     ^
lxc.c: In function ‘Container_get_keys’:
lxc.c:903:5: error: ISO C90 forbids mixed declarations and code [-Werror=declaration-after-statement]
     char* value = (char*) malloc(sizeof(char)*len + 1);
     ^
cc1: some warnings being treated as errors
error: command 'gcc' failed with exit status 1
Makefile:472: recipe for target 'all' failed
make[3]: *** [all] Error 1
make[3]: Leaving directory '/home/masami/codes/lxc/src/python-lxc'
Makefile:394: recipe for target 'all-recursive' failed
make[2]: *** [all-recursive] Error 1
make[2]: Leaving directory '/home/masami/codes/lxc/src'
Makefile:338: recipe for target 'all' failed
make[1]: *** [all] Error 2
make[1]: Leaving directory '/home/masami/codes/lxc/src'
Makefile:484: recipe for target 'all-recursive' failed
make: *** [all-recursive] Error 1

build env:
distribution: Arch Linux
gcc version 4.9.1 20140903 (prerelease) (GCC)

Signed-off-by: Masami Ichikawa <masami256@gmail.com>
Acked-by: Stéphane Graber <stgraber@ubuntu.com>