During sbcl build: cannot fork with multiple threads running

[Paul F. Dietz]

While building the latest sbcl on an x86-64 platform (Ubuntu 16.04), I sometimes (not always) get a failure with this message:

[...]
While evaluating the form starting at line 168, column 0
  of #P"/home/pdietz/sbcl-sbcl/src/cold/compile-cold-sbcl.lisp":
While evaluating the form starting at line 23, column 0
  of #P"/home/pdietz/sbcl-sbcl/make-host-2.lisp":
Unhandled SIMPLE-ERROR in thread #<HOST-SB-THREAD:THREAD "main thread" RUNNING
                                    {1027FD0223}>:
  Cannot fork with multiple threads running.

Backtrace for: #<HOST-SB-THREAD:THREAD "main thread" RUNNING {1027FD0223}>
0: (HOST-SB-DEBUG::DEBUGGER-DISABLED-HOOK #<SIMPLE-ERROR "Cannot fork with multiple threads running." {10015E9AF3}> #<unused argument> :QUIT T)
1: (HOST-SB-DEBUG::RUN-HOOK HOST-SB-EXT:*INVOKE-DEBUGGER-HOOK* #<SIMPLE-ERROR "Cannot fork with multiple threads running." {10015E9AF3}>)
2: (INVOKE-DEBUGGER #<SIMPLE-ERROR "Cannot fork with multiple threads running." {10015E9AF3}>)
3: (ERROR "Cannot fork with multiple threads running.")
4: (HOST-SB-POSIX:FORK)
5: (PARALLEL-MAKE-HOST-2 8)
6: ((LAMBDA NIL :IN "/home/pdietz/sbcl-sbcl/src/cold/compile-cold-sbcl.lisp"))
7: (HOST-SB-INT:SIMPLE-EVAL-IN-LEXENV (THE T (LET ((SB-XC:*COMPILE-PRINT* NIL)) (IF (MAKE-HOST-2-PARALLELISM) (FUNCALL (QUOTE PARALLEL-MAKE-HOST-2) (MAKE-HOST-2-PARALLELISM)) (LET (# # # #) (SETQ HOST-SB-EXT:*EVALUATOR-MODE* :COMPILE) (WITH-MATH-JOURNAL # #) (SB-C::DUMP/RESTORE-INTERESTING-TYPES #))))) #<NULL-LEXENV>)
[...]

sbcl is being built with these options:

export SBCL_MAKE_JOBS=-j8
export SBCL_MAKE_PARALLEL=8
sh make.sh --prefix=/home/pdietz --with-sb-linkable-runtime --with-sb-dynamic-core --dynamic-space-size=12Gb