[PATCH] scan-build: fix arguments for make and gmake

CC and CCX must be set not only for the IgnoreErrors case.

This patch fixes a case when CC is defined in Makefile, because
a value form the environment variable has smaller priority than makefile

The priority of assignments is from least binding to most binding; the
* precedence of assignments is:
* internal definitions
* environment
* makefile(s)
* command line

This bug was found by Roman Kagan <rkagan@parallels.com>.

Signed-off-by: Andrey Vagin <avagin@openvz.org>

Looks good. Please, commit.

Thanks for fixing!