valgrind: update to 3.21.0

Release Notes:
https://valgrind.org/docs/manual/dist.news.html

This improves support for the memory allocator used in musl libc 1.2.2
and later which is currently used by OpenWrt.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
(cherry picked from commit d85013460d)

package/devel/valgrind/patches/130-fix_arm_arch_detection.patch

@@ -6,7 +6,7 @@ Last-Update: 2013-11-30
 
 --- a/configure.ac
 +++ b/configure.ac
-@@ -275,7 +275,7 @@ case "${host_cpu}" in
+@@ -271,7 +271,7 @@ case "${host_cpu}" in
          ARCH_MAX="s390x"
          ;;