Merge pull request #1073 from facebook/hasAttribute

make `DYNAMIC_BMI2` support of `clang` conditional to `__has_attribute()`

lib/common/compiler.h

@@ -64,6 +64,9 @@
 #endif
 
 /* target attribute */
+#ifndef __has_attribute
+  #define __has_attribute(x) 0  /* Compatibility with non-clang compilers. */
+#endif
 #if defined(__GNUC__)
 #  define TARGET_ATTRIBUTE(target) __attribute__((__target__(target)))
 #else
@@ -74,7 +77,7 @@
  * 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)) \