BLD: Add a fallback URL for FreeType

FreeType is available from both Savannah and SourceForge, and sometimes
AppVeyor seems to have trouble downloading from Savannah, so perhaps
this fallback will help. We used to try both these URLs in the pre-Meson
build system.

Author: QuLogic

subprojects/freetype-2.6.1.wrap

@@ -1,5 +1,6 @@
 [wrap-file]
 source_url = https://download.savannah.gnu.org/releases/freetype/freetype-old/freetype-2.6.1.tar.gz
+source_fallback_url = https://downloads.sourceforge.net/project/freetype/freetype2/2.6.1/freetype-2.6.1.tar.gz
 source_filename = freetype-2.6.1.tar.gz
 source_hash = 0a3c7dfbda6da1e8fce29232e8e96d987ababbbf71ebc8c75659e4132c367014