[gimp] m4macros: Windows may have a versioned directory for headers.

[Jehan <jehanp src gnome org>]

commit 61c11b04c12635fd6aa63cf800b37b24d018fdae
Author: Jehan <jehan girinstud io>
Date:   Tue Aug 6 16:22:32 2019 +0200

    m4macros: Windows may have a versioned directory for headers.
    
    Cf !84. We don't want to just replace the old path without versionned
    python, because I assume it has been set for a reason. So there may be
    machines with a versionned python path, others without. Let's test both
    on Windows.

 m4macros/python3dev.m4 | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)
---
diff --git a/m4macros/python3dev.m4 b/m4macros/python3dev.m4
index 7f2629f548..065b7136c7 100644
--- a/m4macros/python3dev.m4
+++ b/m4macros/python3dev.m4
@@ -222,18 +222,19 @@ dnl function also defines PYTHON_INCLUDES
 AC_DEFUN([AM_CHECK_PYTHON_HEADERS],
 [AC_REQUIRE([AM_PATH_PYTHON3])
 AC_MSG_CHECKING(for headers required to compile python extensions)
-dnl Win32 doesn't have a versioned directory for headers
-if test "$PYTHON_PLATFORM" != "win32"; then
-  py_versiondir="/python${PYTHON_VERSION}"
-else
-  py_versiondir=
-fi
 dnl deduce PYTHON_INCLUDES
 py_prefix=`$PYTHON -c "import sys; print(sys.prefix)"`
 py_exec_prefix=`$PYTHON -c "import sys; print(sys.exec_prefix)"`
 PYTHON_INCLUDES=`$PKG_CONFIG --cflags-only-I python-${PYTHON_VERSION}`
 if test "$py_prefix" != "$py_exec_prefix"; then
-  PYTHON_INCLUDES="$PYTHON_INCLUDES -I${py_exec_prefix}/include${py_versiondir}"
+  py_versiondir="${py_exec_prefix}/include/python${PYTHON_VERSION}"
+  dnl Win32 doesn't always have a versioned directory for headers
+  if test "$PYTHON_PLATFORM" = "win32"; then
+    if test -d "${py_versiondir}" ; then
+        py_versiondir=${py_exec_prefix}/include
+    fi
+  fi
+  PYTHON_INCLUDES="$PYTHON_INCLUDES -I${py_versiondir}"
 fi
 AC_SUBST(PYTHON_INCLUDES)
 dnl check if the headers exist: