Fix simarm build for newer gcc's

runtime/platform/globals.h

Index: runtime/platform/globals.h
diff --git a/runtime/platform/globals.h b/runtime/platform/globals.h
index 148343e229a4df81e88b22af9b832bdeadfc0aa9..a18bc8764edef5aefb9fd13b31045cec54d3c514 100644
--- a/runtime/platform/globals.h
+++ b/runtime/platform/globals.h
@@ -280,7 +280,7 @@ typedef simd128_value_t fpu_register_t;
 #error Automatic compiler detection failed.
 #endif
 
-// DART_UNUSED inidicates to the compiler that a variable/typedef is expected
+// DART_UNUSED indicates to the compiler that a variable or typedef is expected
 // to be unused and disables the related warning.
 #ifdef __GNUC__
 #define DART_UNUSED __attribute__((unused))
@@ -288,6 +288,14 @@ typedef simd128_value_t fpu_register_t;
 #define DART_UNUSED
 #endif
 
+// DART_USED indicates to the compiler that a global variable or typedef is used
+// disables e.g. the gcc warning "unused-variable"
+#ifdef __GNUC__
+#define DART_USED __attribute__((used))
+#else
+#define DART_USED
+#endif
+
 // DART_NORETURN indicates to the compiler that a function does not return.
 // It should be used on functions that unconditionally call functions like
 // exit(), which end the program. We use it to avoid compiler warnings in