Fix virtual environment creation when bootstrapping build environments with a standalone Python (#505)

Per
#381 (comment)
this should stop the build bootsrapping script from crashing when
running the build with a standalone Python distribution (which was..
really annoying me).

Author: zanieb

build-linux.py

@@ -21,7 +21,7 @@
 def bootstrap():
     BUILD.mkdir(exist_ok=True)
 
-    venv.create(VENV, with_pip=True)
+    venv.create(VENV, with_pip=True, symlinks=True)
 
     subprocess.run([str(PIP), "install", "-r", str(REQUIREMENTS)], check=True)