GNUmakefile: enable support for CC env variable to use e.g. clang

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
util.h: fix MAX_URI_SIZE sizeof usage

Fix for :

inc/request.h:131:14: error: sizeof on pointer operation will return
 size of 'char *' instead of 'char [9]' [-Werror,-Wsizeof-array-decay]

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
s3.c: fix potential null pointer dereference

Fix for scan-build report:

387  (*gb)->prev->next = buf;

     25 Access to field 'next' results in a dereference of a null
        pointer (loaded from field 'prev')

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
Fix some non-ANSI function declaration

Add void in case no function parameters are declared.

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
Merge pull request #2 from ceph/wip-da-SCA

Some fixes from SCA runs

Reviewed-by: Sage Weil <sage@inktank.com>