Document that we support srfi-87 and add it to %cond-expand-features.

* module/ice-9/boot-9.scm (%cond-expand-features): Add srfi-87.

* doc/ref/srfi-modules.texi (SRFI-0): Add srfi-87 to the list of core
  features.
  (SRFI-87): New node.

doc/ref/srfi-modules.texi

@@ -54,6 +54,7 @@ get the relevant SRFI documents from the SRFI home page
 * SRFI-62::                     S-expression comments.
 * SRFI-67::                     Compare procedures
 * SRFI-69::                     Basic hash tables.
+* SRFI-87::                     => in case clauses.
 * SRFI-88::                     Keyword objects.
 * SRFI-98::                     Accessing environment variables.
 * SRFI-105::                    Curly-infix expressions.
@@ -156,6 +157,7 @@ srfi-39
 srfi-55
 srfi-61
 srfi-62
+srfi-87
 srfi-105
 @end example
 
@@ -5040,6 +5042,14 @@ Answer a hash value appropriate for equality predicate @code{equal?},
 @code{hash} is a backwards-compatible replacement for Guile's built-in
 @code{hash}.
 
+@node SRFI-87
+@subsection SRFI-87 => in case clauses
+@cindex SRFI-87
+
+Starting from version 2.0.6, Guile's core @code{case} syntax supports
+@code{=>} in clauses, as specified by SRFI-87/R7RS.
+@xref{Conditionals}.
+
 @node SRFI-88
 @subsection SRFI-88 Keyword Objects
 @cindex SRFI-88

module/ice-9/boot-9.scm

@@ -4044,6 +4044,7 @@ when none is available, reading FILE-NAME with READER."
     srfi-55  ;; require-extension
     srfi-61  ;; general cond clause
     srfi-62  ;; s-expression comments
+    srfi-87  ;; => in case clauses
     srfi-105 ;; curly infix expressions
     ))