$LDFLAGS not affecting libraries linked by libmpi

[minrk]

Background information

What version of Open MPI are you using? (e.g., v4.1.6, v5.0.1, git branch name and hash, etc.)

v5.0.5

Describe how Open MPI was installed (e.g., from a source/distribution tarball, from a git clone, from an operating system distribution package, etc.)

build from distribution tarball

Please describe the system on which you are running

• Operating system/version: linux
• Computer hardware: CI (Azure, x86)
• Network type: N/A

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Details of the problem

When investigating #12921 where libmpi is linked to libcudart despite being unused, we were curious about why libcudart was not being stripped since we have -Wl,--as-needed in $LDFLAGS.

Looking at the link command for libmpi, it looks like:

x86_64-conda-linux-gnu-cc -shared  -fPIC -DPIC  $lots_of.o  -Wl,--whole-archive $lots_of.a \
  -Wl,--no-whole-archive  -Wl,-rpath -Wl,$WORK/opal/.libs -Wl,-rpath -Wl,$WORK/3rd-party/openpmix/src/.libs -Wl,-rpath -Wl,$PREFIX/lib \
  -L$WORK/3rd-party/openpmix/src/.libs -L$PREFIX/lib -lucc -lcudart \
  $WORK/opal/.libs/libopen-pal.so -lucp -lucs -lucm -luct -lpthread -lrt \
  $WORK/3rd-party/openpmix/src/.libs/libpmix.so -lm -lutil -ldl -levent_core -levent_pthreads -lhwloc  \
  # the next line is $LDFLAGS \
  -march=nocona -mtune=haswell -fstack-protector-strong -O2 -Wl,-O2 -Wl,--sort-common -Wl,--as-needed -Wl,-z -Wl,relro -Wl,-z -Wl,now -Wl,--disable-new-dtags -Wl,--gc-sections -Wl,--allow-shlib-undefined -Wl,-rpath -Wl,$PREFIX/lib -Wl,-rpath-link -Wl,$PREFIX/lib  \
  -pthread -Wl,-soname -Wl,libmpi.so.40 -o .libs/libmpi.so.40.40.5

where it seems relevant that $LDFLAGS comes after the libraries being linked, which I think means -Wl,--as-needed does not get applied to libcudart or any of the libraries being linked into libmpi. It is possible that there is a fix as simple as moving $LDFLAGS earlier in the link command, but I am not sure if that would have any undesirable consequences.