[PATCH v2] drm/i915: fix build issue when using clang

[Tong Zhang]

drm/i915 adds some extra cflags, namely -Wall, which causes
instances of -Wformat-security to appear when building with clang, even
though this warning is turned off kernel-wide in the main Makefile:

> drivers/gpu/drm/i915/gt/intel_gt.c:983:2: error: format string is not a string literal (potentially insecure) [-Werror,-Wformat-security]
>         GEM_TRACE("ERROR\n");
>         ^~~~~~~~~~~~~~~~~~~~
> ./drivers/gpu/drm/i915/i915_gem.h:76:24: note: expanded from macro 'GEM_TRACE'
>  #define GEM_TRACE(...) trace_printk(__VA_ARGS__)
>                        ^~~~~~~~~~~~~~~~~~~~~~~~~
> ./include/linux/kernel.h:369:3: note: expanded from macro 'trace_printk'
>                 do_trace_printk(fmt, ##__VA_ARGS__);    \
>                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> ./include/linux/kernel.h:383:30: note: expanded from macro 'do_trace_printk'
>                 __trace_bprintk(_THIS_IP_, trace_printk_fmt, ##args);   \
>                                           ^~~~~~~~~~~~~~~~
>drivers/gpu/drm/i915/gt/intel_gt.c:983:2: note: treat the string as an argument to avoid this

This does not happen with GCC because it does not enable
-Wformat-security with -Wall. Disable -Wformat-security within the i915
Makefile so that these warnings do not show up with clang.

Signed-off-by: Tong Zhang <ztong0001@xxxxxxxxx>
---

v2: revise commit message

 drivers/gpu/drm/i915/Makefile | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/gpu/drm/i915/Makefile b/drivers/gpu/drm/i915/Makefile
index 1b62b9f65196..c04e05a3d39f 100644
--- a/drivers/gpu/drm/i915/Makefile
+++ b/drivers/gpu/drm/i915/Makefile
@@ -13,6 +13,7 @@
 # will most likely get a sudden build breakage... Hopefully we will fix
 # new warnings before CI updates!
 subdir-ccflags-y := -Wall -Wextra
+subdir-ccflags-y += -Wno-format-security
 subdir-ccflags-y += -Wno-unused-parameter
 subdir-ccflags-y += -Wno-type-limits
 subdir-ccflags-y += -Wno-missing-field-initializers
-- 
2.25.1