make3:fix: Disable parallel builds

Unfortunately, we ran into build non-determinism, causing random
target-hash mismatches. In particular, we noticed this when a hash
mismatch fired after removing some dead code from build_jconsole.sh.

By diffing the xtrace, i.e. `set +x`, results with and without the
change, we confirmed that the executed commands were exactly the same;
however, a quick inspection using diffoscope on the two output
directories revealed differences, not in jconsole, but in libj.so.

The issue seems to be that build outputs are colocated with source
files, meaning that parallel builds end up clobbering each other's
object files.

Author: B. Wilson

jbuild.scm

@@ -179,7 +179,8 @@
     (native-inputs `(("toolchain" ,toolchain)))
     (inputs (cons* libedit libomp jsoftware-auxiliary-files extra-inputs))
     (arguments
-     `(#:parallel-tests? #f
+     `(#:parallel-build? #f
+       #:parallel-tests? #f
        #:tests? #f
        #:modules (((ice-9 ftw) #:select (scandir))
                   ((ice-9 popen) #:select (open-pipe* close-pipe))
@@ -501,7 +502,7 @@ that are not already well understood.")
                     ("LDFLAGS" "-lsleef"))))
 
 (define j (apply j-package j-base-args))
-(define %j-target-hash "tihgvwf7oqyi3cg5p4gregjby42odlrkobumroa6nb7cuphrsrya")
+(define %j-target-hash "har6llk2rv3bwh3gao3qr3ue3dkmm6n4agvmkjhkes3iku2zjngq")
 
 (match (program-arguments)
   ;; Don't execute anything if loading in repl