make: allow to change a compiler

clang-analyzer sets the environment variable CC
scan-build -plist-html --use-analyzer /usr/bin/clang make

Signed-off-by: Andrey Vagin <avagin@openvz.org>
bitopts: add a size sufix for ambiguous instructions

clang requires that.

In file included from arch/x86/cpu.c:9:
arch/x86/include/asm/bitops.h:24:15: error: ambiguous instructions
require an explicit suffix (could be 'btsw', 'btsl', or 'btsq')
        asm volatile("bts %1,%0" : ADDR : "Ir" (nr) : "memory");
clang: add an exception for BUG_ON_HANDLER
cr-show: avoid double free for pstree items
mount: handle errors by the right way

Free all allocated objects and return a negative value
sk-packet: handle errors of xmalloc
socket: handle errors of xmalloc
sockets: free all allocated objected in case of any error
parasite: don't set ret if it is not going to be read

pie/parasite.c:308:3: warning: Value stored to 'ret' is never read
                ret = -1;
ipc_ns: free allocated objects at the end

ipc_ns.c:464:3: warning: Memory is never released; potential leak of
memory pointed to by 'values'
                return;
                ^
1 warning generated.
cr-restore: remove extra initialization of variables

cr-restore.c:1795:2: warning: Value stored to 'restore_task_vma_len' is
never read
        restore_task_vma_len    = 0;
        ^                         ~
cr-restore.c:1796:2: warning: Value stored to 'restore_thread_vma_len'
is never read
        restore_thread_vma_len  = 0;
files: handle errors from fcntl()

files.c:159:21: error: comparison of unsigned expression < 0 is always
false [-Werror,-Wtautological-compare]
        if (p->fown.signum < 0) {
            ~~~~~~~~~~~~~~ ^ ~
pstree: fix error handling

pstree.c:273:3: warning: Value stored to 'ret' is never read
                ret = 0;
                ^     ~