Moving bool include hacks into a dedicated header file.

This was inspired (in the initial commit [1]) by a header from
`msgpack` [2] (and also some help from StackOverflow [3] about
`_MSC_VER` and Matthew Brett's pydagogue doc [4]).

The "last" modification (in [5]) diverges from the original ([2])
by using `char` instead of `int` as the `bool` alias on Windows.
This is so that we can remain true to the binary interface.

[1]: 833643f
[2]: https://github.com/msgpack/msgpack-c/blob/b02c6beb4dfc28b9651ac78e583d2273aef679a7/include/msgpack/sysdep.h#L180-L195
[3]: https://stackoverflow.com/a/5850405/1068170
[4]: http://matthew-brett.github.io/pydagogue/python_msvc.html
[5]: 6fb9da2

src/bezier/include/bezier/bool_patch.h

@@ -0,0 +1,44 @@
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef BEZIER_BOOL_PATCH_H
+#define BEZIER_BOOL_PATCH_H
+
+#if defined (__cplusplus)
+extern "C" {
+#elif !defined (_MSC_VER)
+#include <stdbool.h>
+#endif
+
+#if !defined (__cplusplus) && defined (_MSC_VER)
+#  if !defined (FALSE)
+#    define FALSE (0)
+#  endif
+#  if !defined (TRUE)
+#    define TRUE (!FALSE)
+#  endif
+#  if _MSC_VER >= 1800
+#    include <stdbool.h>
+#  else
+//   NOTE: We must use `char` because it is 1 byte, as `bool` is
+//         in C99 and later (which is what `gfortran` uses).
+#    define bool char
+#    define true TRUE
+#    define false FALSE
+#  endif
+#endif
+
+#if defined (__cplusplus)
+}
+#endif
+
+#endif /* BEZIER_BOOL_PATCH_H */

src/bezier/include/bezier/curve.h

@@ -13,28 +13,10 @@
 #ifndef BEZIER_CURVE_H
 #define BEZIER_CURVE_H
 
+#include "bezier/bool_patch.h"
+
 #if defined (__cplusplus)
 extern "C" {
-#elif !defined (_MSC_VER)
-#include <stdbool.h>
-#endif
-
-#if !defined (__cplusplus) && defined (_MSC_VER)
-#  if !defined (FALSE)
-#    define FALSE (0)
-#  endif
-#  if !defined (TRUE)
-#    define TRUE (!FALSE)
-#  endif
-#  if _MSC_VER >= 1800
-#    include <stdbool.h>
-#  else
-//   NOTE: We must use `char` because it is 1 byte, as `bool` is
-//         in C99 and later (which is what `gfortran` uses).
-#    define bool char
-#    define true TRUE
-#    define false FALSE
-#  endif
 #endif
 
 void evaluate_curve_barycentric(

src/bezier/include/bezier/curve_intersection.h

@@ -13,28 +13,10 @@
 #ifndef BEZIER_CURVE_INTERSECTION_H
 #define BEZIER_CURVE_INTERSECTION_H
 
+#include "bezier/bool_patch.h"
+
 #if defined (__cplusplus)
 extern "C" {
-#elif !defined (_MSC_VER)
-#include <stdbool.h>
-#endif
-
-#if !defined (__cplusplus) && defined (_MSC_VER)
-#  if !defined (FALSE)
-#    define FALSE (0)
-#  endif
-#  if !defined (TRUE)
-#    define TRUE (!FALSE)
-#  endif
-#  if _MSC_VER >= 1800
-#    include <stdbool.h>
-#  else
-//   NOTE: We must use `char` because it is 1 byte, as `bool` is
-//         in C99 and later (which is what `gfortran` uses).
-#    define bool char
-#    define true TRUE
-#    define false FALSE
-#  endif
 #endif
 
 enum BoxIntersectionType {

src/bezier/include/bezier/helpers.h

@@ -13,28 +13,10 @@
 #ifndef BEZIER_HELPERS_H
 #define BEZIER_HELPERS_H
 
+#include "bezier/bool_patch.h"
+
 #if defined (__cplusplus)
 extern "C" {
-#elif !defined (_MSC_VER)
-#include <stdbool.h>
-#endif
-
-#if !defined (__cplusplus) && defined (_MSC_VER)
-#  if !defined (FALSE)
-#    define FALSE (0)
-#  endif
-#  if !defined (TRUE)
-#    define TRUE (!FALSE)
-#  endif
-#  if _MSC_VER >= 1800
-#    include <stdbool.h>
-#  else
-//   NOTE: We must use `char` because it is 1 byte, as `bool` is
-//         in C99 and later (which is what `gfortran` uses).
-#    define bool char
-#    define true TRUE
-#    define false FALSE
-#  endif
 #endif
 
 void cross_product(double *vec0, double *vec1, double *result);