[PATCH] Makefile: fix use of -j without an argument

[Matheus Tavares Bernardino <quic_mathbern@quicinc.com>]

Our Makefile massages the given make arguments to invoke ninja
accordingly. One key difference is that ninja will parallelize by
default, whereas make only does so with -j<n> or -j. The make man page
says that "if the -j option is given without an argument, make will not
limit the number of jobs that can run simultaneously". We use to support
that by replacing -j with "" (empty string) when calling ninja, so that
it would do its auto-parallelization based on the number of CPU cores.

This was accidentally broken at d1ce2cc95b (Makefile: preserve
--jobserver-auth argument when calling ninja, 2024-04-02),
causing `make -j` to fail:

$ make -j V=1
  /usr/bin/ninja -v   -j -d keepdepfile all | cat
  make  -C contrib/plugins/ V="1" TARGET_DIR="contrib/plugins/" all
  ninja: fatal: invalid -j parameter
  make: *** [Makefile:161: run-ninja] Error

Let's fix that and indent the touched code for better readability.

Signed-off-by: Matheus Tavares Bernardino <quic_mathbern@quicinc.com>
---
 Makefile | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/Makefile b/Makefile
index 183756018f..d299c14dab 100644
--- a/Makefile
+++ b/Makefile
@@ -142,8 +142,12 @@ MAKE.k = $(findstring k,$(firstword $(filter-out --%,$(MAKEFLAGS))))
 MAKE.q = $(findstring q,$(firstword $(filter-out --%,$(MAKEFLAGS))))
 MAKE.nq = $(if $(word 2, $(MAKE.n) $(MAKE.q)),nq)
 NINJAFLAGS = $(if $V,-v) $(if $(MAKE.n), -n) $(if $(MAKE.k), -k0) \
-        $(or $(filter -l% -j%, $(MAKEFLAGS)), $(if $(filter --jobserver-auth=%, $(MAKEFLAGS)),, -j1)) \
-        -d keepdepfile
+        $(if $(filter -j, $(MAKEFLAGS)) \
+	     ,, \
+	     $(or \
+	          $(filter -l% -j%, $(MAKEFLAGS)), \
+	          $(if $(filter --jobserver-auth=%, $(MAKEFLAGS)),, -j1)) \
+        ) -d keepdepfile
 ninja-cmd-goals = $(or $(MAKECMDGOALS), all)
 ninja-cmd-goals += $(foreach g, $(MAKECMDGOALS), $(.ninja-goals.$g))
 
-- 
2.37.2