make it possible to build without the obnoxious forced -j to make

Rework --with-parallelism to not add any extra -j to make if 0
or --without is used. This requires explicit -j usage, which
- builds even compilerplugins in parallel
- builds 'make -C sw/' in parallel (since you don't forget the -j)
- avoids jobserver disabling if -j is explicitly passed to the toplevel make

IMO this is just a relic of the old build system and the option should
be dumped altogether, but I don't feel like arguing right now.

Change-Id: I71479391bcfc84aa5e9fd9696880702da496d45c

Makefile.in

@@ -55,6 +55,8 @@ include $(BUILDDIR)/config_$(gb_Side).mk
 
 export GMAKE_OPTIONS?=-r$(if $(verbose)$(VERBOSE),,s)$(value $(MAKEFLAGS))
 
+PARALLELISM_OPTION := $(if $(filter-out 0,$(PARALLELISM)),-j $(PARALLELISM),)
+
 #
 # Partial Build
 #
@@ -62,13 +64,13 @@ define gb_Top_GbuildModuleRules
 .PHONY: $(1) $(1).all $(1).build $(1).check $(1).clean $(1).showdeliverables $(1).subsequentcheck
 
 $(1): bootstrap fetch
-	cd $(SRCDIR)/$(2) && $(GNUMAKE) -j $(PARALLELISM) $(GMAKE_OPTIONS)
+	cd $(SRCDIR)/$(2) && $(GNUMAKE) $(PARALLELISM_OPTION) $(GMAKE_OPTIONS)
 
 $(1).build $(1).check $(1).clean $(1).showdeliverables $(1).subsequentcheck:
-	cd $(SRCDIR)/$(2) && $(GNUMAKE) -j $(PARALLELISM) $(GMAKE_OPTIONS) $$(patsubst $(1).%,%,$$@)
+	cd $(SRCDIR)/$(2) && $(GNUMAKE) $(PARALLELISM_OPTION) $(GMAKE_OPTIONS) $$(patsubst $(1).%,%,$$@)
 
 $(1).all: bootstrap fetch
-	$(GNUMAKE) -j $(PARALLELISM) $(GMAKE_OPTIONS) -f $(SRCDIR)/Makefile.gbuild $(WORKDIR)/Module/$(1) $(if $(CROSS_COMPILING),,$(WORKDIR)/Module/check/$(1) $(WORKDIR)/Module/slowcheck/$(1))
+	$(GNUMAKE) $(PARALLELISM_OPTION) $(GMAKE_OPTIONS) -f $(SRCDIR)/Makefile.gbuild $(WORKDIR)/Module/$(1) $(if $(CROSS_COMPILING),,$(WORKDIR)/Module/check/$(1) $(WORKDIR)/Module/slowcheck/$(1))
 
 endef
 
@@ -121,7 +123,7 @@ gbuild_TARGETS := AllLangHelp \
 
 # build a generic gbuild target
 $(foreach target,$(gbuild_TARGETS),$(target)_% $(foreach module,$(gbuild_modules),$(target)_$(module)/%)):
-	$(GNUMAKE) -j $(PARALLELISM) $(GMAKE_OPTIONS) -f $(SRCDIR)/Makefile.gbuild $@
+	$(GNUMAKE) $(PARALLELISM_OPTION) $(GMAKE_OPTIONS) -f $(SRCDIR)/Makefile.gbuild $@
 
 #
 # Clean
@@ -221,15 +223,15 @@ build: bootstrap fetch $(if $(CROSS_COMPILING),cross-toolset)
 ifneq ($(filter-out WNT MACOSX IOS ANDROID,$(OS)),)
 	mkdir -p $(INSTDIR) && install-gdb-printers -a $(INSTDIR) -c
 endif
-	$(GNUMAKE) -j $(PARALLELISM) $(GMAKE_OPTIONS) -f $(SRCDIR)/Makefile.gbuild $(build_goal)
+	$(GNUMAKE) $(PARALLELISM_OPTION) $(GMAKE_OPTIONS) -f $(SRCDIR)/Makefile.gbuild $(build_goal)
 ifeq ($(OS),IOS)
-	$(GNUMAKE) -j $(PARALLELISM) $(GMAKE_OPTIONS) ios
+	$(GNUMAKE) $(PARALLELISM_OPTION) $(GMAKE_OPTIONS) ios
 endif
 
 build-non-l10n-only build-l10n-only build-nocheck check debugrun help slowcheck translations unitcheck subsequentcheck packageinfo: build
 
 cross-toolset: bootstrap fetch
-	$(GNUMAKE) gb_Side=build -j $(PARALLELISM) $(GMAKE_OPTIONS) -f $(SRCDIR)/Makefile.gbuild build-tools
+	$(GNUMAKE) gb_Side=build $(PARALLELISM_OPTION) $(GMAKE_OPTIONS) -f $(SRCDIR)/Makefile.gbuild build-tools
 
 
 #

configure.ac

@@ -12373,7 +12373,7 @@ AC_MSG_CHECKING([for number of processors to use])
 # plain --with-parallelism is just the default
 if test -n "$with_parallelism" -a "$with_parallelism" != "yes"; then
     if test "$with_parallelism" = "no"; then
-        PARALLELISM=1
+        PARALLELISM=0
     else
         PARALLELISM=$with_parallelism
     fi
@@ -12397,10 +12397,7 @@ else
         esac
 
         # If we hit the catch-all case, but /proc/cpuinfo doesn't exist or has an
-        # unexpected format, 'wc -l' will have returned 0.
-        if test "$PARALLELISM" -eq 0; then
-            PARALLELISM=1
-        fi
+        # unexpected format, 'wc -l' will have returned 0 (and we won't use -j at all).
     fi
 fi
 
@@ -12414,7 +12411,11 @@ if test "$no_parallelism_make" = "YES" && test $PARALLELISM -gt 1; then
     fi
 fi
 
-AC_MSG_RESULT([$PARALLELISM])
+if test $PARALLELISM -eq 0; then
+    AC_MSG_RESULT([explicit make -j option needed])
+else
+    AC_MSG_RESULT([$PARALLELISM])
+fi
 AC_SUBST(PARALLELISM)
 
 #