[PATCH for-4.14] compilers/clang: always use _Static_assert with clang

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

All versions of clang used by Xen support _Static_assert, so use it
unconditionally when building Xen with clang.

No functional change expected.

Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
Not sure whether this fully qualifies as a bugfix, as the current
behavior should also work fine under clang. Note that all versions of
clang from 3.5 to trunk (11) seem to return __GNUC__ == 4 and
__GNUC_MINOR__ == 2.
---
 xen/include/xen/lib.h | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/xen/include/xen/lib.h b/xen/include/xen/lib.h
index e5b0a007b8..076bcfb67d 100644
--- a/xen/include/xen/lib.h
+++ b/xen/include/xen/lib.h
@@ -25,7 +25,9 @@
 #define BUG_ON(p)  do { if (unlikely(p)) BUG();  } while (0)
 #define WARN_ON(p) do { if (unlikely(p)) WARN(); } while (0)
 
-#if __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 6)
+/* All clang versions supported by Xen have _Static_assert. */
+#if defined(__clang__) || \
+    (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 6))
 /* Force a compilation error if condition is true */
 #define BUILD_BUG_ON(cond) ({ _Static_assert(!(cond), "!(" #cond ")"); })
 
-- 
2.26.2