bug#68195: flite fails to build on core-updates

[Simon South]

On core-updates (4d1436b0ea65) the flite package is failing to build,
with log output like

  making ../build/aarch64-linux-gnu/lib/libflite.so
  make[1]: *** No rule to make target 'flite_voice_list.c', needed by 'all'.  
Stop.
  make[1]: *** Waiting for unfinished jobs....
  make: *** [config/common_make_rules:133: 
build/aarch64-linux-gnu/obj//.make_build_dirs] Error 2

This is caused by the upgrade to make 4.4 along with what appears to be
an error in one of the project's makefiles.

The workaround is to build flite with parallel build jobs disabled,
using e.g. "./pre-inst-env guix build --cores=1 flite".

The underlying issue appears to be a misuse of the ".NOTPARALLEL"
special make target in the project's main/Makefile.  Changing line 107
from

  .NOTPARALLEL: $(ALL)

to simply

  .NOTPARALLEL:

solves the problem: The entire project builds in parallel except for
targets in the "main" subfolder, which are built serially instead.
(These targets have to be built serially as they delete and re-create
the same "flite_voice_list.o" object file in different ways.)

With make versions 4.3 and earlier any prerequisites specified for
".NOTPARALLEL" ("$(ALL)" as shown above) were ignored, and make would
unconditionally build all remaining targets in series.

With make 4.4 this behaviour has changed and the prerequisites list is
now honoured.  However, this doesn't specify a list of targets to build
serially, as it seems the flite authors expected.  Rather,

  If the .NOTPARALLEL special target has prerequisites, then each of
  those prerequisites will be considered a target and all prerequisites
  of these targets will be run serially.[0]

That is, it is the _prerequisites_ of the specified targets and not the
targets themselves that are built serially.  The targets themselves may
still be built in parallel, which is how the upgrade to make 4.4 has
caused this problem to appear.

I'll add for completeness that getting clever and changing the makefile
with something like

  notparallel: $(ALL)
  .NOTPARALLEL: notparallel

doesn't work, as (for one reason or another) this doesn't sufficiently
protect the targets from clobbering one another.

-- 
Simon South
simon@simonsouth.net

[0] https://www.gnu.org/software/make/manual/html_node/Parallel-Disable.html