gdb: bump to 8.2.1

gdb: bump to 8.2.1

PR build/23516 (gdb build error under msys+mingw: strip can't handle gdb-add-index.exe)
PR build/23623 (install-strip fails)
PR rust/23626 (gdb crashes in upstream rust nil-enum test)
PR rust/23650 (rust field name access error mentions "foo")
PR gdb/23663 (gdb 8.1.1: undefined rpl_stat function with musl toolchains)
PR python/23669 (gdb.execute("show commands") doesn't work)
PR python/23714 (Command repetition stops working after gdb.execute)
PR gdb/23838 (8.2 regression for invalid -data-directory)
PR gdb/23974 ("info os" crash when specifying invalid object)
PR gdb/23999 (SYMBOL_LANGUAGE assertion failure on AIX)
PR gdb/24003 (Error when binary searching CUs for a specific DIE when using DWZ)

Signed-off-by: Koen Vandeputte <koen.vandeputte@ncentric.com>