fix out of tree doc build (#20519)

closes #20457

Author: tkelman

doc/Makefile

@@ -32,32 +32,32 @@ cleanall: clean
 html: deps
 	@echo "Building HTML documentation."
 ifneq ($(OS),WINNT)
-	$(JULIA_EXECUTABLE) make.jl -- deploy
+	$(JULIA_EXECUTABLE) $(SRCDIR)/make.jl -- deploy
 else
 # work around issue #11727, windows output redirection breaking on buildbot
-	$(JULIA_EXECUTABLE) make.jl -- deploy > docbuild.log 2>&1
+	$(JULIA_EXECUTABLE) $(SRCDIR)/make.jl -- deploy > docbuild.log 2>&1
 	@cat docbuild.log
 endif
 	@echo "Build finished. The HTML pages are in _build/html."
 
 pdf: deps
 	@echo "Building PDF documentation."
-	$(JULIA_EXECUTABLE) make.jl -- pdf
+	$(JULIA_EXECUTABLE) $(SRCDIR)/make.jl -- pdf
 	@echo "Build finished."
 
 linkcheck: deps
 	@echo "Checking external documentation links."
-	$(JULIA_EXECUTABLE) make.jl -- linkcheck
+	$(JULIA_EXECUTABLE) $(SRCDIR)/make.jl -- linkcheck
 	@echo "Checks finished."
 
 doctest: deps
 	@echo "Running all embedded 'doctests'."
-	$(JULIA_EXECUTABLE) --color=yes make.jl -- doctest
+	$(JULIA_EXECUTABLE) --color=yes $(SRCDIR)/make.jl -- doctest
 	@echo "Checks finished."
 
 check: deps
 	@echo "Running all embedded 'doctests' and checking external links."
-	$(JULIA_EXECUTABLE) --color=yes make.jl -- doctest linkcheck
+	$(JULIA_EXECUTABLE) --color=yes $(SRCDIR)/make.jl -- doctest linkcheck
 	@echo "Checks finished."
 
 .PHONY: deps

doc/make.jl

@@ -11,7 +11,7 @@ using Documenter
 
 baremodule GenStdLib end
 isdefined(:build_sysimg) || @eval module BuildSysImg
-    include(joinpath(JULIA_HOME, "..", "..", "contrib", "build_sysimg.jl"))
+    include(joinpath(@__DIR__, "..", "contrib", "build_sysimg.jl"))
 end
 
 # Documenter Setup.
@@ -113,7 +113,7 @@ const PAGES = [
 ]
 
 makedocs(
-    build     = "_build/html/en",
+    build     = joinpath(pwd(), "_build/html/en"),
     modules   = [Base, Core, BuildSysImg],
     clean     = false,
     doctest   = "doctest" in ARGS,