Document SRFI-23

* doc/ref/srfi-modules.texi: mention that we support SRFI 23
 * module/ice-9/boot-9.scm (%cond-expand-features): add srfi-23

doc/ref/srfi-modules.texi

@@ -35,6 +35,7 @@ get the relevant SRFI documents from the SRFI home page
 * SRFI-17::                     Generalized set!
 * SRFI-18::                     Multithreading support
 * SRFI-19::                     Time/Date library.
+* SRFI-23::                     Error reporting
 * SRFI-26::                     Specializing parameters
 * SRFI-27::                     Sources of Random Bits
 * SRFI-30::                     Nested multi-line block comments
@@ -3135,6 +3136,11 @@ Conversion is locale-dependent on systems that support it
 locale.
 @end defun
 
+@node SRFI-23
+@subsection SRFI-23 - Error Reporting
+@cindex SRFI-23
+
+The SRFI-23 @code{error} procedure is always available.
 
 @node SRFI-26
 @subsection SRFI-26 - specializing parameters

module/ice-9/boot-9.scm

@@ -3404,6 +3404,7 @@ module '(ice-9 q) '(make-q q-length))}."
     srfi-4   ;; homogenous numeric vectors
     srfi-6   ;; open-input-string etc, in the guile core
     srfi-13  ;; string library
+    srfi-23  ;; `error` procedure
     srfi-14  ;; character sets
     srfi-55  ;; require-extension
     srfi-61  ;; general cond clause