make DYNAMIC_BMI2 support of clang conditional to __has_attribute()

to support older clang versions such as 3.4

diff --git a/lib/common/compiler.h b/lib/common/compiler.h
index bb87301263fd9129d34f39ea6978ae33e856beb5..a6044c86147e89a9d29a4144aec3f6ad89d14628 100644 (file)
--- a/lib/common/compiler.h
+++ b/lib/common/compiler.h
@@ -74,7 +74,7 @@
  * Enabled for clang & gcc >=4.8 on x86 when BMI2 isn't enabled by default.
  */
 #ifndef DYNAMIC_BMI2
-  #if defined(__clang__)    \
+  #if (defined(__clang__) && __has_attribute(__target__)) \
       || (defined(__GNUC__) \
           && (__GNUC__ >= 5 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 8))) \
       && (defined(__x86_64__) || defined(_M_X86)) \