bpo-28552: Fix distutils.sysconfig for empty sys.executable (GH-12875)

bpo-28552, bpo-7774: Fix distutils.sysconfig if sys.executable is
None or an empty string: use os.getcwd() to initialize project_base.

Fix also the distutils build command: don't use sys.executable if
it's evaluated as false (None or empty string).

command/build.py

@@ -116,7 +116,7 @@ class build(Command):
             self.build_scripts = os.path.join(self.build_base,
                                               'scripts-%d.%d' % sys.version_info[:2])
 
-        if self.executable is None:
+        if self.executable is None and sys.executable:
             self.executable = os.path.normpath(sys.executable)
 
         if isinstance(self.parallel, str):

sysconfig.py

@@ -28,7 +28,12 @@ BASE_EXEC_PREFIX = os.path.normpath(sys.base_exec_prefix)
 if "_PYTHON_PROJECT_BASE" in os.environ:
     project_base = os.path.abspath(os.environ["_PYTHON_PROJECT_BASE"])
 else:
-    project_base = os.path.dirname(os.path.abspath(sys.executable))
+    if sys.executable:
+        project_base = os.path.dirname(os.path.abspath(sys.executable))
+    else:
+        # sys.executable can be empty if argv[0] has been changed and Python is
+        # unable to retrieve the real program name
+        project_base = os.getcwd()
 
 
 # python_build: (Boolean) if true, we're either building Python or