+ :SOURCE-NAMESTRING Namestring-Form
+ Attaches the value returned by the Namestring-Form to the internal
+ debug-source information as the namestring of the source file. Normally
+ the namestring of the input-file for COMPILE-FILE is used: this option
+ can be used to provide source-file information for functions compiled
+ using COMPILE, or to override the input-file of COMPILE-FILE.
+
+ If both an outer and an inner WITH-COMPILATION-UNIT provide a
+ SOURCE-NAMESTRING, the inner one takes precedence. Unaffected
+ by :OVERRIDE.
+
+ This is an SBCL-specific extension.
+