Issue #7774: Set sys.executable to an empty string if argv[0] has been
set to an non existent program name and Python is unable to retrieve the real
program name.

Fix also sysconfig: if sys.executable is an empty string, use the current
working directory.
diff --git a/Lib/sysconfig.py b/Lib/sysconfig.py
index 69264d2..a11a412 100644
--- a/Lib/sysconfig.py
+++ b/Lib/sysconfig.py
@@ -84,7 +84,12 @@
 _EXEC_PREFIX = os.path.normpath(sys.exec_prefix)
 _CONFIG_VARS = None
 _USER_BASE = None
-_PROJECT_BASE = os.path.dirname(realpath(sys.executable))
+if sys.executable:
+    _PROJECT_BASE = os.path.dirname(realpath(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 = realpath(os.getcwd())
 
 if os.name == "nt" and "pcbuild" in _PROJECT_BASE[-8:].lower():
     _PROJECT_BASE = realpath(os.path.join(_PROJECT_BASE, pardir))