Require 2.29 if building glibc for RISC-V64

Signed-off-by: Alexey Neyman <stilor@att.net>

config/arch/riscv.in

@@ -13,6 +13,7 @@
 ## select GCC_REQUIRE_7_or_later
 ## select BINUTILS_REQUIRE_2_28_or_later
 ## select GDB_REQUIRE_8_0_or_later if DEBUG_GDB
+## select GLIBC_REQUIRE_2_29_or_later if LIBC_GLIBC
 
 ## help The RISC-V architecture, as defined by:
 ## help     http://www.riscv.org/