In the sysimage.mk Makefile, set the JULIA_NUM_THREADS=1 environm…

…ent variable when running the `generate_precompile.jl` script (#44281)

contrib/generate_precompile.jl

@@ -1,5 +1,9 @@
 # This file is a part of Julia. License is MIT: https://julialang.org/license
 
+if Threads.nthreads() != 1
+    @warn "Running this file with multiple Julia threads may lead to a build error" Threads.nthreads()
+end
+
 if Base.isempty(Base.ARGS) || Base.ARGS[1] !== "0"
 Sys.__init_build()
 # Prevent this from being put into the Main namespace

sysimage.mk

@@ -77,6 +77,7 @@ define sysimg_builder
 $$(build_private_libdir)/sys$1-o.a $$(build_private_libdir)/sys$1-bc.a : $$(build_private_libdir)/sys$1-%.a : $$(build_private_libdir)/sys.ji
 	@$$(call PRINT_JULIA, cd $$(JULIAHOME)/base && \
 	if ! JULIA_BINDIR=$$(call cygpath_w,$(build_bindir)) WINEPATH="$$(call cygpath_w,$$(build_bindir));$$$$WINEPATH" \
+			JULIA_NUM_THREADS=1 \
 			$$(call spawn, $3) $2 -C "$$(JULIA_CPU_TARGET)" --output-$$* $$(call cygpath_w,$$@).tmp $$(JULIA_SYSIMG_BUILD_FLAGS) \
 			--startup-file=no --warn-overwrite=yes --sysimage $$(call cygpath_w,$$<) $$(call cygpath_w,$$(JULIAHOME)/contrib/generate_precompile.jl) $(JULIA_PRECOMPILE); then \
 		echo '*** This error is usually fixed by running `make clean`. If the error persists$$(COMMA) try `make cleanall`. ***'; \