Fix #76137: config.guess/config.sub do not recognize RISC-V

These had their latest update more than three years ago, so there may
be even more issues.  Since the config project[1] does not have any
versioning, we're grabbing the most recent HEAD.

[1] <http://git.savannah.gnu.org/gitweb/?p=config.git;a=summary>

Author: cmb69

NEWS

@@ -40,6 +40,7 @@ PHP                                                                        NEWS
   . Fixed bug #75765 (Fatal error instead of Error exception when base class is
     not found). (Timur Ibragimov)
   . Fixed bug #76198 (Wording: "iterable" is not a scalar type). (Levi Morrison)
+  . Fixed bug #76137 (config.guess/config.sub do not recognize RISC-V). (cmb)
 
 - BCMath:
   . Fixed bug #66364 (BCMath bcmul ignores scale parameter). (cmb)