Make distutils error messages more helpful (#11599).

When running external programs such as a C compiler and getting an
error code, distutils only prints the program name.  With this change,
one can get the full command line by setting the DISTUTILS_DEBUG
environment variable.

This should have no compatibility issues, unless there are tools
that depend on the exact format of distutils debug messages.
diff --git a/Misc/NEWS b/Misc/NEWS
index 2fce437..4e915f5 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -44,6 +44,10 @@
   as documented.  The pattern and source keyword parameters are left as
   deprecated aliases.
 
+- Issue #11599: When an external command (e.g. compiler) fails, distutils now
+  prints out the whole command line (instead of just the command name) if the
+  environment variable DISTUTILS_DEBUG is set.
+
 - Issue #4931: distutils should not produce unhelpful "error: None" messages
   anymore.  distutils.util.grok_environment_error is kept but doc-deprecated.