toolchain: gdb: Update to version 15.2
See news file for changes:
https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=blob_plain;f=gdb/NEWS;hb=gdb-15.1-release
This requires a C++17 compiler compatible compiler.
Link: https://github.com/openwrt/openwrt/pull/16665
Signed-off-by: Hauke Mehrtens <[email protected]>