Motivation for this change

Building openjdk on my Linux box failed because the build process wrongly took the existence of /usr/include/sys/sdt.h as a sign that dtrace should be enabled. Which then failed because sys/sdt.h cannot be found during build.

hotspot/make/linux/makefiles/dtrace.make contains:

# But it does have a SystemTap dtrace compatible sys/sdt.h
ifneq ($(ALT_SDT_H),)
  SDT_H_FILE = $(ALT_SDT_H)
else
  SDT_H_FILE = /usr/include/sys/sdt.h
endif
DTRACE_ENABLED = $(shell test -f $(SDT_H_FILE) && echo $(SDT_H_FILE))
REASON = "$(SDT_H_FILE) not found"

ifneq ($(DTRACE_ENABLED),)
  CFLAGS += -DDTRACE_ENABLED
endif

It's not a problem on NixOS because /usr/include/sys/sdt.h doesn't exist there. So let's not even try to find that file, it shouldn't be used anyway.

Things done

Please check what applies. Note that these are not hard requirements but mereley serve as information for reviewers.

• Tested using sandboxing
  (nix.useSandbox on NixOS,
  or option build-use-sandbox in nix.conf
  on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • Linux
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Fits CONTRIBUTING.md.