Update pip-2020-resolver of PexBuilder

[thinker0]

Fix pip-2020-resolver of PexBuilder

• Fix failed to resolve a requirement

export CC=/usr/bin/clang
export CXX=/usr/bin/clang++

echo $CC $CXX
./bazel_configure.py

/usr/bin/clang /usr/bin/clang++
Platform Darwin
Using C compiler          :	/usr/bin/clang (12.0.5)
Using C++ compiler        :	/usr/bin/clang++ (12.0.5)
Using C preprocessor      :	/usr/bin/cpp (12.0.5)
Using C++ preprocessor    :	/usr/bin/cpp (12.0.5)
Using linker              :	/usr/bin/ld
Using JDK                 :	/Users/thinker0/.sdkman/candidates/java/current
Using Automake            :	/usr/local/Cellar/automake/1.16.5/bin/automake (1.16.5)
Using Autoconf            :	/usr/local/Cellar/autoconf/2.71/bin/autoconf (2.71)
Using Make                :	/usr/bin/make (3.81)
Using Python3             :	/usr/local/Cellar/python@3.8/3.8.12_1/Frameworks/Python.framework/Versions/3.8/bin/python3.8 (3.8.12)
Using Libtool             :	/usr/local/Cellar/libtool/2.4.6_4/bin/glibtool (2.4.6)
Using archiver            :	/usr/bin/ar
Using coverage tool       :	/usr/bin/gcov
Using ant                 :	/usr/local/Cellar/ant/1.10.12/bin/ant
dwp                       :	not found, but ok
Using nm                  :	/usr/bin/nm
objcopy                   :	not found, but ok
Using objdump             :	/usr/bin/objdump
Using strip               :	/usr/bin/strip

[thinker0]

Fix #3686

[thinker0]

^________^; Thanks @nicknezis

[thinker0]

Add #3734