Update download locations in build_usd.py to avoid issues

due to Let's Encrypt root certificate expiration on systems
with OpenSSL version 1.0.2.

This change updates build_usd.py to download library sources
from alternate locations that are not affected by the
certificate issues. These are still "official" locations
listed on the websites for these libraries.

(Internal change: 2191554)

build_scripts/build_usd.py

@@ -685,13 +685,13 @@ def InstallZlib(context, force, buildArgs):
 # boost
 
 if MacOS():
-    BOOST_URL = "https://downloads.sourceforge.net/project/boost/boost/1.70.0/boost_1_70_0.tar.gz"
+    BOOST_URL = "https://boostorg.jfrog.io/artifactory/main/release/1.70.0/source/boost_1_70_0.tar.gz"
     BOOST_VERSION_FILE = "include/boost/version.hpp"
 elif Linux():
     if Python3():
-        BOOST_URL = "https://downloads.sourceforge.net/project/boost/boost/1.70.0/boost_1_70_0.tar.gz"
+        BOOST_URL = "https://boostorg.jfrog.io/artifactory/main/release/1.70.0/source/boost_1_70_0.tar.gz"
     else:
-        BOOST_URL = "https://downloads.sourceforge.net/project/boost/boost/1.66.0/boost_1_66_0.tar.gz"
+        BOOST_URL = "https://boostorg.jfrog.io/artifactory/main/release/1.66.0/source/boost_1_66_0.tar.gz"
     BOOST_VERSION_FILE = "include/boost/version.hpp"
 elif Windows():
     # The default installation of boost on Windows puts headers in a versioned 
@@ -701,7 +701,7 @@ def InstallZlib(context, force, buildArgs):
     #
     # boost 1.70 is required for Visual Studio 2019. For simplicity, we use
     # this version for all older Visual Studio versions as well.
-    BOOST_URL = "https://downloads.sourceforge.net/project/boost/boost/1.70.0/boost_1_70_0.tar.gz"
+    BOOST_URL = "https://boostorg.jfrog.io/artifactory/main/release/1.70.0/source/boost_1_70_0.tar.gz"
     BOOST_VERSION_FILE = "include/boost-1_70/boost/version.hpp"
 
 def InstallBoost_Helper(context, force, buildArgs):
@@ -947,7 +947,7 @@ def InstallJPEG_Lib(context, force, buildArgs):
 ############################################################
 # TIFF
 
-TIFF_URL = "https://download.osgeo.org/libtiff/tiff-4.0.7.zip"
+TIFF_URL = "https://gitlab.com/libtiff/libtiff/-/archive/Release-v4-0-7/libtiff-Release-v4-0-7.tar.gz"
 
 def InstallTIFF(context, force, buildArgs):
     with CurrentWorkingDirectory(DownloadURL(TIFF_URL, context, force)):
@@ -979,7 +979,7 @@ def InstallTIFF(context, force, buildArgs):
 ############################################################
 # PNG
 
-PNG_URL = "https://downloads.sourceforge.net/project/libpng/libpng16/older-releases/1.6.29/libpng-1.6.29.tar.gz"
+PNG_URL = "https://github.com/glennrp/libpng/archive/refs/tags/v1.6.29.tar.gz"
 
 def InstallPNG(context, force, buildArgs):
     with CurrentWorkingDirectory(DownloadURL(PNG_URL, context, force)):