Raise on signal exit in Status#exit_code

spec/std/process/status_spec.cr

@@ -27,7 +27,13 @@ describe Process::Status do
     Process::Status.new(exit_status(128)).exit_code.should eq 128
     Process::Status.new(exit_status(255)).exit_code.should eq 255
 
-    status_for(:interrupted).exit_code.should eq({% if flag?(:unix) %}0{% else %}LibC::STATUS_CONTROL_C_EXIT.to_i32!{% end %})
+    if {{ flag?(:unix) }}
+      expect_raises(RuntimeError, "Abnormal exit has no exit code") do
+        status_for(:interrupted).exit_code
+      end
+    else
+      status_for(:interrupted).exit_code.should eq({% if flag?(:unix) %}0{% else %}LibC::STATUS_CONTROL_C_EXIT.to_i32!{% end %})
+    end
   end
 
   it "#success?" do

src/process/status.cr

@@ -205,9 +205,13 @@ class Process::Status
     {% end %}
   end
 
-  # If `normal_exit?` is `true`, returns the exit code of the process.
+  # Returns the exit code of the process if it exited normally.
+  #
+  # Raises if the status describes an abnormal exit.
   def exit_code : Int32
     {% if flag?(:unix) %}
+      raise RuntimeError.new("Abnormal exit has no exit code") unless normal_exit?
+
       # define __WEXITSTATUS(status) (((status) & 0xff00) >> 8)
       (@exit_status & 0xff00) >> 8
     {% else %}