Use GNU mirror FTP for downloading related libs

Author: mxamin

build_support/releases.py

@@ -60,7 +60,7 @@ def latest_zlib_release():
 
 
 def latest_libiconv_release():
-    return latest_release_from_html('https://ftp.gnu.org/pub/gnu/libiconv', re.compile('libiconv-(?P<version>.*).tar.gz'))
+    return latest_release_from_html('https://ftpmirror.gnu.org/libiconv', re.compile('libiconv-(?P<version>.*).tar.gz'))
 
 
 def latest_libxml2_release():

build_support/static_build.py

@@ -182,7 +182,7 @@ def _ensure_source_archives(self):
                 version=self.builder.libiconv_version,
                 env_label='PYXMLSEC_LIBICONV_VERSION',
                 default_url=latest_libiconv_release,
-                version_url=lambda v: f'https://ftp.gnu.org/pub/gnu/libiconv/libiconv-{v}.tar.gz',
+                version_url=lambda v: f'https://ftpmirror.gnu.org/libiconv/libiconv-{v}.tar.gz',
             ),
             self._ensure_source(
                 name='libxml2',