app, icons: use the Python executable found by pythonmod.find_installation().

We already search for a compatible Python version in the root meson file, no
need to look up Python 3 again in the PATH, each time we run an external Python
script in the build.

This should hopefully fix #9687.

app/dialogs/meson.build

@@ -2,13 +2,13 @@ welcome_dialog_data_h = custom_target('welcome-dialog-data-h',
                                       input : [meson.project_source_root() / 'tools/generate-welcome-dialog-data.py',
                                                meson.project_source_root() / 'desktop/org.gimp.GIMP.appdata.xml.in.in'],
                                       output : ['welcome-dialog-data.h'],
-                                      command : ['python3', '@INPUT0@', gimp_version, '--header'],
+                                      command : [python, '@INPUT0@', gimp_version, '--header'],
                                       capture: true)
 welcome_dialog_data_c = custom_target('welcome-dialog-data-c',
                                       input : [meson.project_source_root() / 'tools/generate-welcome-dialog-data.py',
                                                meson.project_source_root() / 'desktop/org.gimp.GIMP.appdata.xml.in.in'],
                                       output : ['welcome-dialog-data.c'],
-                                      command : ['python3', '@INPUT0@', gimp_version],
+                                      command : [python, '@INPUT0@', gimp_version],
                                       capture: true)
 
 libappdialogs_sources = [

icons/Color/meson.build

@@ -23,7 +23,7 @@ foreach install : install_icons
   dup_icons = []
   foreach input : inputs
     input = '../icon-lists/@0@.list'.format(input)
-    cmd = run_command('python3', '-c',
+    cmd = run_command(python, '-c',
                       py_cmd.format(indir, suffix, input),
                       check: true)
     dup_icons += cmd.stdout().strip().split(',')

icons/Symbolic/meson.build

@@ -28,7 +28,7 @@ foreach install : install_icons
   dup_icons = []
   foreach input : inputs
     input = '../icon-lists/@0@.list'.format(input)
-    cmd = run_command('python3', '-c',
+    cmd = run_command(python, '-c',
                       py_cmd.format(indir, suffix, input),
                       check: true)
     dup_icons += cmd.stdout().strip().split(',')

icons/meson.build

@@ -60,7 +60,7 @@ foreach theme : themes
       foreach input : inputs
         icon_list = 'icon-lists/@0@.list'.format(input)
         py_cmd = 'print(",".join([line.strip() for line in open("@0@") if line.strip() != "" and line.strip()[0] != "#"]))'
-        cmd = run_command('python3', '-c',
+        cmd = run_command(python, '-c',
                           py_cmd.format(icon_list),
                           check: true)
         dup_icons += cmd.stdout().strip().split(',')

meson.build

@@ -1609,12 +1609,12 @@ endif
 
 
 # git-version.h is already present and not generated if dist tarball
-is_git_repository = run_command('python3', '-c',
+is_git_repository = run_command(python, '-c',
   'import sys,os; sys.exit(0 if os.path.exists(".git") else 1)',
   check: false
 ).returncode() == 0
 
-has_version_h = run_command('python3', '-c',
+has_version_h = run_command(python, '-c',
   'import sys,os; sys.exit(0 if os.path.exists("git-version.h") else 1)',
   check: false
 ).returncode() == 0