[gimp] configure: some Python test cleanup/improvements.

[Jehan <jehanp src gnome org>]

commit 521ff83cba8899bf74790f2d5e389d878c655cdc
Author: Jehan <jehan girinstud io>
Date:   Wed Jul 24 14:02:41 2019 +0200

    configure: some Python test cleanup/improvements.
    
    In particular, when header check fails, Python option is disabled.
    
    Also let's use pkg-config to search for the Python include directory.
    The reason is that include/python{version} is not always
    true. On my system in particular, python3.7 was in `include/python3.7m`.

 configure.ac           |   8 +-
 m4macros/python3dev.m4 |   2 +-
 m4macros/pythondev.m4  | 245 -------------------------------------------------
 3 files changed, 4 insertions(+), 251 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index ce93366138..2a5881661b 100644
--- a/configure.ac
+++ b/configure.ac
@@ -82,7 +82,6 @@ m4_define([poppler_required_version], [0.69.0])
 m4_define([poppler_data_required_version], [0.4.9])
 m4_define([pycairo_required_version], [1.0.2])
 m4_define([pygtk_required_version], [2.10.4])
-# m4_define([python2_required_version], [2.5.0])
 m4_define([python3_required_version], [3.6.0])
 m4_define([rsvg_required_version], [2.40.6])
 m4_define([webkitgtk_required_version], [2.20.3])
@@ -181,7 +180,6 @@ PANGOCAIRO_REQUIRED_VERSION=pangocairo_required_version
 PERL_REQUIRED_VERSION=perl_required_version
 POPPLER_REQUIRED_VERSION=poppler_required_version
 POPPLER_DATA_REQUIRED_VERSION=poppler_data_required_version
-# PYTHON2_REQUIRED_VERSION=python2_required_version
 PYTHON3_REQUIRED_VERSION=python3_required_version
 RSVG_REQUIRED_VERSION=rsvg_required_version
 WEBKITGTK_REQUIRED_VERSION=webkitgtk_required_version
@@ -216,7 +214,6 @@ AC_SUBST(PERL_REQUIRED_VERSION)
 AC_SUBST(POPPLER_REQUIRED_VERSION)
 AC_SUBST(POPPLER_DATA_REQUIRED_VERSION)
 AC_SUBST(PYTHON3_REQUIRED_VERSION)
-# AC_SUBST(PYTHON2_REQUIRED_VERSION)
 AC_SUBST(RSVG_REQUIRED_VERSION)
 AC_SUBST(WEBKITGTK_REQUIRED_VERSION)
 AC_SUBST(WEBP_REQUIRED_VERSION)
@@ -2256,7 +2253,8 @@ m4_define([pycheck_error], [
   - $1
       *** Please install $2, or skip building the python scripting extension by
       *** passing --disable-python to configure (but then you will not be able
-      *** to use scripts for GIMP that are written in Python)."])
+      *** to use scripts for GIMP that are written in Python)."
+  enable_python="no"])
 
 if test "x$enable_python" != xno; then
   enable_python="yes"
@@ -3037,7 +3035,7 @@ Optional Plug-Ins:
   Heif >= 1.4.0:             $have_libheif_1_4_0
   PDF (export):              $have_cairo_pdf
   Print:                     $enable_print
-  Python 3:                $enable_python
+  Python 3:                  $enable_python
   TWAIN (Win32):             $os_win32
   Webpage:                   $have_webkit
   WMF:                       $have_libwmf
diff --git a/m4macros/python3dev.m4 b/m4macros/python3dev.m4
index 14e22c39cb..7f2629f548 100644
--- a/m4macros/python3dev.m4
+++ b/m4macros/python3dev.m4
@@ -231,7 +231,7 @@ fi
 dnl deduce PYTHON_INCLUDES
 py_prefix=`$PYTHON -c "import sys; print(sys.prefix)"`
 py_exec_prefix=`$PYTHON -c "import sys; print(sys.exec_prefix)"`
-PYTHON_INCLUDES="-I${py_prefix}/include${py_versiondir}"
+PYTHON_INCLUDES=`$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}"
 fi