When building with clang, disable -Wformat-security for

sys/dev/hpt27xx/osm_bsd.c, since it gets the following warnings:

sys/dev/hpt27xx/osm_bsd.c:1180:25: error: format string is not a string literal (potentially insecure) [-Werror,-Wformat-security]
            S_IRUSR | S_IWUSR, driver_name);
                               ^~~~~~~~~~~
@/dev/hpt27xx/hpt27xx_config.h:46:21: note: expanded from:
#define driver_name hpt27xx_driver_name
                    ^~~~~~~~~~~~~~~~~~~

Since 'hpt27xx_driver_name' is a constant string symbol (coming from the
proprietary hpt27xx_lib.o file), there is no security problem.

Because this driver is provided by the vendor, and applying changes
requires re-certification and other bureaucratic exercises, just disable
the warning for now.

MFC after:	1 week

sys/conf/kern.mk

@@ -23,6 +23,7 @@ NO_WSHIFT_COUNT_OVERFLOW=	-Wno-shift-count-overflow
 NO_WUNUSED_VALUE=		-Wno-unused-value
 NO_WSELF_ASSIGN=		-Wno-self-assign
 NO_WUNNEEDED_INTERNAL_DECL=	-Wno-unneeded-internal-declaration
+NO_WFORMAT_SECURITY=		-Wno-format-security
 # Several other warnings which might be useful in some cases, but not severe
 # enough to error out the whole kernel build.  Display them anyway, so there is
 # some incentive to fix them eventually.

sys/modules/hpt27xx/Makefile

@@ -12,3 +12,6 @@ hpt27xx_lib.o:
 	uudecode -p < ${HPT27XX}/$(MACHINE_ARCH)-elf.hpt27xx_lib.o.uu > ${.TARGET}
 
 .include <bsd.kmod.mk>
+
+CWARNFLAGS.osm_bsd.c=	${NO_WFORMAT_SECURITY}
+CWARNFLAGS+=		${CWARNFLAGS.${.IMPSRC:T}}