ARM: add AArch32 support and new vcvt instructions

src/base/atomicops_internals_arm_gcc.h

Index: src/base/atomicops_internals_arm_gcc.h
diff --git a/src/base/atomicops_internals_arm_gcc.h b/src/base/atomicops_internals_arm_gcc.h
index 069b1ffa88387046f812fdcd50ffd71a32808025..55024a0537590da95e3b254ab1ac2e71768efa10 100644
--- a/src/base/atomicops_internals_arm_gcc.h
+++ b/src/base/atomicops_internals_arm_gcc.h
@@ -57,9 +57,11 @@ inline void MemoryBarrier() {
 
 // An ARM toolchain would only define one of these depending on which
 // variant of the target architecture is being used. This tests against
-// any known ARMv6 or ARMv7 variant, where it is possible to directly
+// any known ARMv6, ARMv7 or ARMv8 variant, where it is possible to directly
 // use ldrex/strex instructions to implement fast atomic operations.
-#if defined(__ARM_ARCH_7__) || defined(__ARM_ARCH_7A__) || \
+#if defined(__ARM_ARCH_8__) || defined(__ARM_ARCH_8A__) || \
+    defined(__ARM_ARCH_8R__) || defined(__ARM_ARCH_8M__) || \
+    defined(__ARM_ARCH_7__) || defined(__ARM_ARCH_7A__) || \
     defined(__ARM_ARCH_7R__) || defined(__ARM_ARCH_7M__) || \
     defined(__ARM_ARCH_6__) || defined(__ARM_ARCH_6J__) || \
     defined(__ARM_ARCH_6K__) || defined(__ARM_ARCH_6Z__) || \