This patch fixes PR bootstrap/106472 by adding a missing dependency
to Makefile.def to allow make bootstrap when configured using
"--enable-languages=go" (and not using make with multiple threads).

Tested on x86-64-pc-linux-gnu.  Ok for mainline?


2022-07-30  Roger Sayle  <roger@nextmovesoftware.com>

ChangeLog
        PR bootstrap/106472
        * Makefile.def (dependencies): Make configure-target-libgo depend
        upon all-target-libbacktrace.


Thanks in advance,
Roger
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