Revert "compat: Use standard bool to resolve C99+ keyword conflicts (#18)"

This reverts commit 4885126.

Author: wojciech-graj

src/doomtype.h

@@ -65,19 +65,22 @@
 
 #include <inttypes.h>
 
-#if (defined(__STDC_VERSION__) && __STDC_VERSION__ >= 199901L) || defined(__cplusplus)
-// For C99+ and C++, use the standard boolean type
-#include <stdbool.h>
+#ifdef __cplusplus
+
+// Use builtin bool type with C++.
+
+typedef bool bool;
+
 #else
-// For older C standards, use the original custom enum
-typedef enum { false = 0, true = 1 } bool;
-#endif
 
-// The original enum also defined an 'undef' state.
-// left for compatibility
-enum {
-    undef = 0xFFFFFFFF
-};
+typedef enum
+{
+    false	= 0,
+    true	= 1,
+	undef	= 0xFFFFFFFF
+} bool;
+
+#endif
 
 typedef uint8_t byte;