As of version 13.x GDB uses libtool for linking instead of g++ these
take different arguments for static linking. Commit 6146b5a6 ("use
-all-static when building a static gdb") attempted to deal with this but
had the effect of causing older GDB versions to fail to build
statically. Add a new internal flag GDB_CC_LD_LIBTOOL and use this to
decide whether to pass `-static` or `-all-static`.
Fixes#2053
Signed-off-by: Chris Packham <judge.packham@gmail.com>