Use add_dll_directory to add DLL folders on Windows

We can now set the WEASYPRINT_DLL_DIRECTORIES environment variable to list
folders where DLL can be found.

Fix #1435.

weasyprint/text/ffi.py

@@ -6,6 +6,8 @@
 
 """
 
+import os
+
 import cffi
 
 ffi = cffi.FFI()
@@ -387,21 +389,32 @@ def _dlopen(ffi, *names):
     return ffi.dlopen(names[0])  # pragma: no cover
 
 
+if hasattr(os, 'add_dll_directory'):
+    dll_directories = os.getenv(
+        'WEASYPRINT_DLL_DIRECTORIES',
+        'C:\\Program Files\\GTK3-Runtime Win64\\bin').split(';')
+    for dll_directory in dll_directories:
+        try:
+            os.add_dll_directory(dll_directory)
+        except (OSError, FileNotFoundError):
+            pass
+
 gobject = _dlopen(
     ffi, 'gobject-2.0-0', 'gobject-2.0', 'libgobject-2.0-0',
-    'libgobject-2.0.so.0', 'libgobject-2.0.dylib')
+    'libgobject-2.0.so.0', 'libgobject-2.0.dylib',  'libgobject-2.0-0.dll')
 pango = _dlopen(
     ffi, 'pango-1.0-0', 'pango-1.0', 'libpango-1.0-0', 'libpango-1.0.so.0',
-    'libpango-1.0.dylib')
+    'libpango-1.0.dylib', 'libpango-1.0-0.dll')
 harfbuzz = _dlopen(
     ffi, 'harfbuzz', 'harfbuzz-0.0', 'libharfbuzz-0',
-    'libharfbuzz.so.0', 'libharfbuzz.so.0', 'libharfbuzz.0.dylib')
+    'libharfbuzz.so.0', 'libharfbuzz.so.0', 'libharfbuzz.0.dylib',
+    'libharfbuzz-0.dll')
 fontconfig = _dlopen(
-    ffi, 'fontconfig-1', 'fontconfig', 'libfontconfig', 'libfontconfig-1.dll',
-    'libfontconfig.so.1', 'libfontconfig-1.dylib')
+    ffi, 'fontconfig-1', 'fontconfig', 'libfontconfig', 'libfontconfig.so.1',
+    'libfontconfig-1.dylib', 'libfontconfig-1.dll')
 pangoft2 = _dlopen(
     ffi, 'pangoft2-1.0-0', 'pangoft2-1.0', 'libpangoft2-1.0-0',
-    'libpangoft2-1.0.so.0', 'libpangoft2-1.0.dylib')
+    'libpangoft2-1.0.so.0', 'libpangoft2-1.0.dylib', 'libpangoft2-1.0-0.dll')
 
 gobject.g_type_init()