`TBB_LIB` on Windows adds `--disable-new-dtags`, which Rtools' linkers reject

[jgabry]

In stan-dev/cmdstanr#1286 I'm experimenting with CmdStanR building
the model methods it loads into R against RcppParallel's oneTBB when that package is installed
(so rstan/rstanarm/brms and cmdstanr can share a process), which means setting TBB_INC and
TBB_LIB on Windows.

While working on that Claude and I ran into this issue.

When TBB_LIB is set, make/compiler_flags adds -Wl,--disable-new-dtags
to LDFLAGS_TBB on every OS except macOS:

# MacOS ld does not support --disable-new-dtags
ifneq ($(OS),Darwin)
  LDFLAGS_TBB_DTAGS ?= -Wl,--disable-new-dtags
endif

According to Claude:

--disable-new-dtags controls DT_RPATH versus DT_RUNPATH in ELF
binaries. PE linkers don't know it, so on Windows every link fails. With
Rtools 4.5 (x86_64, binutils ld):

ld.exe: unrecognized option '--disable-new-dtags'
ld.exe: use the --help option for usage information
collect2.exe: error: ld returned 1 exit status

and with Rtools 4.5 for ARM64 (clang 19, lld):

lld: error: unknown argument: --disable-new-dtags
clang-19: error: linker command failed with exit code 1

The flag only matters alongside -rpath, and the block right below already
skips -rpath on Windows, so the same condition should apply to both:

ifneq ($(OS),Darwin)
ifneq ($(OS),Windows_NT)
  LDFLAGS_TBB_DTAGS ?= -Wl,--disable-new-dtags
endif
endif

The workaround we're using for now (in the PR I linked to above):
pass LDFLAGS_TBB_DTAGS= on the make command line (or set it in make/local).

Current Version

v5.4.0 (CmdStan 2.40.0)

[WardBrian]

I think it would be fine to update the makefile as Claude suggests (or invert the condition and just detect Linux?)

I suspect you're the first person using these flags on Windows, since most places you can get a compiled TBB on windows will be built using MSVC which we can't link against

[jgabry]

Ok cool, I can make a PR