#164 make -j16 fails

[Ricardo Buring]

Arguably this is a user error on my part (it is not explicitly written that e.g. make -j16 is allowed, I just tried it out of habit), but using svn revision 6844, running ./configure --with-csl followed by make -j16 fails with errors such as the following:

[x86_64-unknown-ubuntu22.04] CXX   csl-arith01.o
[x86_64-unknown-ubuntu22.04] CXX   csl-arith02.o
[x86_64-unknown-ubuntu22.04] CXX   csl-arith03.o
[x86_64-unknown-ubuntu22.04] CXX   csl-arith04.o
[x86_64-unknown-ubuntu22.04] CXX   csl-arith05.o
[x86_64-unknown-ubuntu22.04] CXX   csl-arith08.o
[x86_64-unknown-ubuntu22.04] CXX   csl-arith06.o
[x86_64-unknown-ubuntu22.04] CXX   csl-arith07.o
[x86_64-unknown-ubuntu22.04] CXX   csl-arith10.o
[x86_64-unknown-ubuntu22.04] CXX   csl-arith09.o
[x86_64-unknown-ubuntu22.04] CXX   csl-arith11.o
[x86_64-unknown-ubuntu22.04] CXX   csl-arith12.o
[x86_64-unknown-ubuntu22.04] CXX   csl-arith13.o
[x86_64-unknown-ubuntu22.04] CXX   csl-arith14.o
[x86_64-unknown-ubuntu22.04] CXX   csl-arith-quad.o
[x86_64-unknown-ubuntu22.04] CXX   csl-isprime.o
[x86_64-unknown-ubuntu22.04] CXX   csl-char.o
In file included from /home/rburing/src/reduce/csl/cslbase/headers.h:82,
                 from /home/rburing/src/reduce/csl/cslbase/arith04.cpp:41:
/home/rburing/src/reduce/csl/cslbase/machine.h:359:10: fatal error: softfloat.h: No such file or directory
  359 | #include "softfloat.h"
      |          ^~~~~~~~~~~~~
In file included from /home/rburing/src/reduce/csl/cslbase/headers.h:82,
                 from /home/rburing/src/reduce/csl/cslbase/arith01.cpp:41:
/home/rburing/src/reduce/csl/cslbase/machine.h:359:10: fatal error: softfloat.h: No such file or directory
  359 | #include "softfloat.h"
      |          ^~~~~~~~~~~~~
In file included from /home/rburing/src/reduce/csl/cslbase/headers.h:82,
                 from /home/rburing/src/reduce/csl/cslbase/arith12.cpp:41:
/home/rburing/src/reduce/csl/cslbase/machine.h:359:10: fatal error: softfloat.h: No such file or directory
  359 | #include "softfloat.h"
      |          ^~~~~~~~~~~~~
In file included from /home/rburing/src/reduce/csl/cslbase/headers.h:82,
                 from /home/rburing/src/reduce/csl/cslbase/arith11.cpp:43:
/home/rburing/src/reduce/csl/cslbase/machine.h:359:10: fatal error: softfloat.h: No such file or directory
  359 | #include "softfloat.h"
      |          ^~~~~~~~~~~~~
In file included from /home/rburing/src/reduce/csl/cslbase/headers.h:82,
                 from /home/rburing/src/reduce/csl/cslbase/arith06.cpp:40:
/home/rburing/src/reduce/csl/cslbase/machine.h:359:10: fatal error: softfloat.h: No such file or directory
  359 | #include "softfloat.h"
      |          ^~~~~~~~~~~~~
In file included from /home/rburing/src/reduce/csl/cslbase/headers.h:82,
                 from /home/rburing/src/reduce/csl/cslbase/arith08.cpp:39:
/home/rburing/src/reduce/csl/cslbase/machine.h:359:10: fatal error: softfloat.h: No such file or directory
  359 | #include "softfloat.h"
      |          ^~~~~~~~~~~~~
compilation terminated.
compilation terminated.
compilation terminated.
compilation terminated.
compilation terminated.
compilation terminated.

Using the plain make (without -j16) does work as expected.