Cross-platformizing MMIO stuff.

MSVC build likely needs some fixes.

src/poly/debugging.h

@@ -23,6 +23,10 @@ namespace debugging {
 // though, so avoid calling it frequently.
 bool IsDebuggerAttached();
 
+// Breaks into the debugger if it is attached.
+// If no debugger is present, a signal will be raised.
+void Break();
+
 }  // namespace debugging
 }  // namespace poly
 

src/poly/debugging_mac.cc

@@ -25,5 +25,11 @@ bool IsDebuggerAttached() {
   return (info.kp_proc.p_flag & P_TRACED) != 0;
 }
 
+// TODO(benvanik): find a more reliable way.
+void Break() {
+  // __asm__("int $3");
+  __builtin_debugtrap();
+}
+
 }  // namespace debugging
 }  // namespace poly

src/poly/debugging_win.cc

@@ -16,5 +16,9 @@ bool IsDebuggerAttached() {
   return IsDebuggerPresent() ? true : false;
 }
 
+void Break() {
+  __debugbreak();
+}
+
 }  // namespace debugging
 }  // namespace poly

src/poly/poly.h

@@ -15,6 +15,7 @@
 #include <poly/byte_order.h>
 #include <poly/config.h>
 #include <poly/cxx_compat.h>
+#include <poly/debugging.h>
 #include <poly/math.h>
 #include <poly/memory.h>
 #include <poly/platform.h>