chore: Mask ARM source if not AARCH64 not defined

runtime/include/arch/aarch64/context.h

@@ -1,4 +1,5 @@
 #pragma once
+#if defined(AARCH64) || defined(aarch64)
 
 #include <assert.h>
 #include "arch/common.h"
@@ -129,11 +130,15 @@ arch_context_switch(struct arch_context *a, struct arch_context *b)
 	             ".align 8\n\t"
 	             "exit%=:\n\t"
 	             :
-	             : [ a ] "r"(a_registers), [ b ] "r"(b_registers), [ av ] "r"(&a->variant), [ bv ] "r"(&b->variant),
+	             : [a] "r"(a_registers), [b] "r"(b_registers), [av] "r"(&a->variant), [bv] "r"(&b->variant),
-	               [ slowpath ] "r"(&arch_context_restore_preempted)
+	               [slowpath] "r"(&arch_context_restore_preempted)
 	             : "memory", "cc", "x0", "x1", "x2", "x3", "x4", "x5", "x6", "x7", "x8", "x9", "x10", "x11", "x12",
 	               "x13", "x14", "x15", "x16", "x17", "x18", "x19", "x20", "x21", "x22", "x23", "x24", "d8", "d9",
 	               "d10", "d11", "d12", "d13", "d14", "d15");
 
 	return 0;
 }
+
+#else
+#warning "Neither AARCH64 nor aarch64 was defined, but aarch64/context.h was included!"
+#endif