Bug 1546169 - Enable 64-bit atomics for more platforms in AtomicOperations-feeling-lucky-gcc.h. r=lth

Differential Revision: https://phabricator.services.mozilla.com/D28394

--HG--
extra : moz-landing-system : lando

js/src/jit/shared/AtomicOperations-feeling-lucky-gcc.h

@@ -42,7 +42,8 @@
 #endif
 
 // 64-bit atomics are not required by the JS spec, and you can compile
-// SpiderMonkey without them.
+// SpiderMonkey without them. 64-bit atomics are required for BigInt
+// support.
 //
 // 64-bit lock-free atomics are required for WebAssembly, but gating in the
 // WebAssembly subsystem ensures that no WebAssembly-supporting platforms need
@@ -69,6 +70,13 @@
 #  endif
 #endif
 
+#ifdef JS_CODEGEN_NONE
+#  ifdef JS_64BIT
+#    define HAS_64BIT_ATOMICS
+#    define HAS_64BIT_LOCKFREE
+#  endif
+#endif
+
 // The default implementation tactic for gcc/clang is to use the newer __atomic
 // intrinsics added for use in C++11 <atomic>.  Where that isn't available, we
 // use GCC's older __sync functions instead.