mbed_chrono: restore asserts

Now that we've got a workaround for ARMC6, asserts can be restored.

Author: kjbracey

platform/mbed_chrono.h

@@ -19,6 +19,7 @@
 #ifndef __MBED_CHRONO_H__
 #define __MBED_CHRONO_H__
 
+#include "mbed_toolchain.h"
 #include <cstdint>
 #include <cassert>
 #include <ratio>
@@ -85,10 +86,7 @@ inline namespace chrono_literals {
 constexpr chrono::deciseconds operator "" _ds(unsigned long long x)
 {
     chrono::deciseconds::rep val = static_cast<chrono::deciseconds::rep>(x);
-    if (val < 0) {
-        assert(false);
-    }
-    assert(static_cast<unsigned long long>(val) == x);
+    assert(val >= 0 && static_cast<unsigned long long>(val) == x);
     return chrono::deciseconds(val);
 }
 
@@ -106,10 +104,7 @@ constexpr chrono::deciseconds operator "" _ds(unsigned long long x)
 constexpr chrono::centiseconds operator "" _cs(unsigned long long x)
 {
     chrono::centiseconds::rep val = static_cast<chrono::centiseconds::rep>(x);
-    if (val < 0) {
-        assert(false);
-    }
-    assert(static_cast<unsigned long long>(val) == x);
+    assert(val >= 0 && static_cast<unsigned long long>(val) == x);
     return chrono::centiseconds(val);
 }